Rubber Molding Methods Offer Essential Functionality

Plastics and Rubber Products have become a common feature in homes. For that matter even Industries have fallen hook, line and sinker for the two. Two major factors like credibility and versatility have been driving their demand. Considering the soaring demand for plastic and rubber products, we have come up with a common platform for all plastic and rubber manufacturers, suppliers, exporters and buyers, to trade with each other at the click of a mouse. A few years back, transactions used to take place ‘on –field’, with both parties sitting face-to-face, before closing the deal. Here, the major plus point is the transaction is taking place ‘on-line’ and you can strike a profitable deal right away. Sitting face-to-face can be done anytime.

The use of rubber has revolutionized much of the world. In fact, without rubber, many of the daily conveniences that most people take for granted would not even be possible, or if possible, they would not operate in the same way. Rubber cushions, isolates, eliminates unwanted vibration, noise, and even offers better traction for moving parts. Rubber is used for an incredibly diverse number of applications. However, there is one key to all of these diverse uses - rubber molding techniques.

Rubber molding is a science unto itself, with a number of different techniques and technologies involved. Through the process of specialized molding techniques, any type of rubber design can be created, from air inlet elbows to locomotive boots, voting machine parts, silicone rings for heart and lung machines, viton seals and much, much more. What sorts of molding techniques are used in the industry, and what does each technique have to offer? Here is a glimpse of the technology behind the functionality that most of us take for granted.

Compression Rubber Molding: This method uses a compression mold to create rubber parts and forms. In essence, this process simply requires that a mold be opened, an uncured slug of rubber be inserted and then sufficient compression be placed on the now-closed mold to shape the rubber into the desired shape. Molds can have a single cavity and two plates, or they can be configured in numerous different ways to create the desired form.

Transfer Rubber Molding: Transfer molding is quite a bit like compression molding, in that it uses a mold to create the final form. However, material is transferred from the "pot" by the force of a plunger and enters channels, or "sprue," and runners to fill the cavities within the mold. This is used to create a wide range of different parts, particularly those where a need for delicate rubber pieces or high-definition pieces is required.

Injection Rubber Molding: Injection molding is used with numerous different materials, including rubber and plastics. It results in pliable parts that are also durable, and is capable of high-speed mass production. Rubber is injected into a mold and the amount is metered to ensure the correct amount is used. This material is injected into a mold, which is secured with a clamp. An incredible diversity of products can be manufactured through the process of injection molding.

The key to having the high-quality rubber components that you need is to choose a company with the utmost experience and expertise in rubber molding techniques. The best option is to choose a firm that offers all three of the abovementioned techniques, as this will ensure that you can have any type of rubber component manufactured that you might require, from delicate rubber items to highly detailed, complex rubber boots. Of course, you should also make sure that the company has experience making similar products, as this will certainly play a role in your satisfaction with your finished rubber pieces.

Discovery of Plastics Towards World Development

Today, plastic is considered one of the greatest inventions in our new generation. It signifies modernity and progress of humanity. Plastic has touched lives of people compared to other breakthroughs in technology. It has replaced old and usual things. Elegant heavy tables and desks have been transformed into lighter structures, with pastel color touches and made homes and offices change their theme. Indeed, plastic fits into the contemporary world. Aside from being light and strong it can be easily molded and it is durable. But have you ever asked yourself how plastics were invented? Everyday, plastics are scattered everywhere, which contributes to health, safety, and security, but have you ever tried searching the origins of plastic?

In 1862, Alexander Parkes made the first ever man made plastic for London's Great International Exhibition. This material, which was made from organic materials that came from cellulose, was first known as Parkisine. Once this material was exposed to heat it could be molded but when cooled, it would retain its shape. Alexander Parkes said that his discovery could do all that rubber can do but at a lower cost. He discovered a material that could be transparent and could also be carved into different shapes. However, it soon lost its limelight as investors had pulled out of the market because of the high value of raw materials used in producing it.

After the discovery of plastic many items were found to be more useful and efficient when made from it. Late 19th century there was a rush on finding a replacement for the ivory used in billiard balls - this was the time that Billiards was extremely popular and the elephant population was being decimated to obtain their ivory. Fortunately, an American inventor named John Wesley Hyatt found the solution using celluloid in 1869. He accidentally spilled a bottle of collodion in his workplace and he discovered that it formed a tough and flexible film. That was when he had the idea of making billiard balls using this new material named collodion, which substituted ivory. But since this material is brittle in nature, billiard balls made from collodion shattered once they hit one another. There was a solution to this problem, which came by adding camphor from laurel tree. Due to this addition, the celluloid was the first thermoplastic or substance that molds when under pressure or heat into shapes that can be retained even after being under heat or pressure.

In 1907, a man-made synthetic was first discovered by Leo Baekeland, a chemist from New York who developed Bakelite or a liquid resin. The Bakelizer, an apparatus made by Baekeland, enabled him to control volatile chemicals when heated and pressurized. This pot-like equipment used by Baekeland developed Bakelite, which hardens rapidly and takes the shape of a container. If hardened, the resin will form a replica of any container where it is placed. Bakelite can be added into any material such as softwood, to make it more effective and more durable. The United States government used Bakelite in its weaponry and war machinery where steel could not be used. It was also used for domestic use such as insulation. Through these uses Bakelite proved itself as a very effective building material. Moreover, Bakelite is resistant to electricity, chemically stable, shatter proof, resistant to heat and it does not discolor, fade or crack when exposed to sea salt or sunlight.

Plastic was later made into different varieties of usable materials like Cellophane, which was discovered by a Swiss engineer named Dr. Jacques Edwin Brandenberger. He came up with an idea for a protective and clear packaging layer during 1900. While sitting at a restaurant, he saw a customer who happened to spill a bottle of wine on the table cloth. A server removed the table cloth and replaced it with another disposing of the soiled one. The Swiss textile engineer swore to dedicate himself to discovering how to apply clear flexible films on the cloth that would keep it safe from such accidents and would make it easier to be cleaned with just a swipe of a towel. He then worked on resolving this issue by utilizing different kinds of materials in experiments up until 1913 when he hit pay dirt with Viscose - known today as Rayon. Brandenberger applied the Viscose to cloth, however the material became hardened and was to brittle for use. Despite his unsuccessful venture in applying his material to cloth he discovered another use for the Viscose. He developed new equipment that would create thin Viscose sheets which later became known as Cellophane. Minor improvements were made to Cellophane in years that followed that allowed it to be used as a clear layer for packaging of any product. Cellophane was the first completely flexible and water resistant wrap.

With the discovery of new plastics came the plastic craze in 1920 as the use of cellophane spread throughout the world. One of the largest companies known as Dupont became a pioneer in discovering other materials made of plastic. A young chemist from Harvard, Wallace Hume Carothers was then the head of Dupont lab. Carothers became responsible for the moisture proofing of Cellophane and during this process discovered a method for creating a new material - Fiber 66 - known commonly today as Nylon. The young chemist saw the promising value of the new discovered tough plastic. Since its discovery the material has been used in widespread fashion including use as a replacement for animal hairs in toothbrushes as well as silk stockings. Carothers demonstrated that by substitution and insertion of elements on the chemical chain, new, durable materials could be discovered and developed. By 1940, the world savored the use of materials like Nylon, Neoprene, Acrylic and other polymers which had taken the place of natural materials.

Another important innovation with plastics was the development of polyvinyl chloride or PVC or vinyl. While working for the B.F. Goodrich company an organic chemist by the name of Waldo Semon attempted to combine rubber and metal. Although its importance was not immediately recognized he later discovered the value of this material as it was inexpensive yet fire resistant, durable and could be molded easily. This material caught the attention of western families for it could last many years in an average living room.

Organic chemists at Imperial Chemical Industries Research Laboratory tested various chemicals in conditions with high pressure. In 1933, these researchers, R.O Gibson and E.W Fawcett discovered polyethylene that made a vast impact throughout the world. These researchers were attempting to discover the reaction of a benzaldehyde and ethylene mixture when suddenly the experiment's testing container leaked and the pressure inside escaped. Upon opening the tube they found a white and waxy substance that looked like a plastic. This was the discovery of polyethylene and soon after compressors were created for large scale production of the product. Since its discovery Polyethylene has been an important material in the history. During World War II, this material was used in cable coatings used underwater and for military applications like radar insulation. It can actually reduce weight of radars to only 600 pounds.

After the war, it was widely used by the general public. It was the first plastic to reach one billion pounds of production in a year in United States and is presently the largest production in the whole world. Nowadays, polyethylene is being used in making soda bottles, grocery bags and milk jugs.

Another plastic known as Silly Putty, was discovered by James Wright, an engineer working for General Electric, when he mixed boric acid and silicon oil. This rubber-like had the ability to bounce 25 percent higher compared to a normal ball made of rubber.

During roughly the same time, a Swiss engineer by the name of George de Mestral had a plastic discovery of his own. He found that when nylon was sewn under infrared light it formed very small yet tough hook-like patterns. These tiny hooks would then catch with soft material to form a very strong hold. Dubbing the new product Velcro, a cross between velour and crochet, he patented the product in 1955 and has developed it into a multi-million dollar industry today.

Since 1950's plastics have grown into a primary industry that made a huge impact in our lives providing us with improvements in packaging, creating many varieties of textiles and giving us the opportunity to produce wonderful new inventions and technologies like cars, television and computers. Since 1976, plastic was considered the most used material all over the world and was included in the best inventions of the century. Thanks to those pioneers who developed the material we are able to enjoy many luxuries of the modern era.

Considerations in Formulating Rubber Products

Rubbers come from two distinct sources: natural rubber, which is created using latex drawn from rubber trees; and synthetic rubber, which is chemically synthesized. Regardless of origin, every rubber is characterized by its ability to withstand very large deformations and then "bounce back" essentially to its original condition. Natural rubber, while used in many products today, has mechanical, chemical and environmental resistance limitations that would make it unusable for many applications; very often synthetic rubbers can be formulated to address these short comings.

There is actually no such thing as standard rubber materials; for each use, there is a custom formulated product that is tailored to meet the precise needs of that application. Rubber is a far more complex material than other materials such as steel or plastic. Whereas steel or plastic typically is the result of melting 3 - 4 materials together, a rubber formulation often consists of 10 - 20 materials blended together. Additionally, several of these components will undergo an irreversible chemical reaction when the rubber is vulcanized during the manufacturing cycle. Because of the sheer number of ingredients and the transforming chemical reactions, there is no realistic way to reverse engineer rubber. Formulating rubber is more "art" than "science".

In formulating a rubber product, there are three types of performance challenges to consider.

1. Dynamic. The one factor that distinguishes rubber from other materials is the very large deformations that it can endure in its applications. Rubber must maintain its properties through a lifetime of dynamic stressing. Rubber needs to be resilient enough to perform its function even after being compressed, stretched or twisted thousands, or even millions of times.
2. Chemical. Rubber is often required to withstand a variety of chemicals. For applications in motors or generators, it must be resistant to gasoline and oils. Some industrial equipment will see a variety of harsh fluids such as cleaning solvents, acids or alkalis. Rubber tubes can have any number of harsh fluids pumped through them. Without proper formulation, a rubber compound could literally dissolve or crumble when faced with these corrosive elements.
3. Environmental. Not only does rubber have to stay flexible for thousands of cycles and possibly withstand corrosive chemicals, but it may also be required to perform in temperature extremes. A good example of this is a car sitting out in a Minnesota winter: during the night, the sealing O-Rings in its engine will be subjected to freezing temperatures. The O-Rings need to seal just as well when that cold engine first starts as they do when the engine reaches its peak temperature.

When these performance challenges are combined, it can create a tremendous (if not impossible) task for the rubber formulator.

The first step in rubber formulation is to develop detailed requirements relating to conditions that the rubber will need to withstand. It is fairly straight forward to identify the mechanical/dynamic requirements; however, chemical and environmental factors are commonly misunderstood. In this case a rubber formulation chemist with a great deal of experience is necessary. The chemist has seen a large variety of applications and can help identify what conditions a product could potentially experience out in the field.

After thoroughly understanding all the requirements, a rubber formulation chemist can derive a recipe of dozens components to create the compound. Rubber formulation is extremely complex and can draw upon literally hundreds of potential variables. Because of the scale of this complexity, there are not many tools and guides to analytically determine the exact formulation that will optimize performance for a given application. Achieving optimum performance with rubber is far more of an "art" than a "science", and requires experienced and knowledgeable formulators.

It is not uncommon for a number of different mixtures to be created and tested before the ideal product is developed. Temperature stressing, fluid immersion, elongation testing, tensile strength, flex-cycling, ozone aging and weathering can be performed in a lab, and this testing provides some indication of the product's performance. However, only testing that duplicates field conditions can be trusted to determine the acceptability of the formulation.

Plastics and Rubber Products have become a common feature in homes. For that matter even Industries have fallen hook, line and sinker for the two. Two major factors like credibility and versatility have been driving their demand. Considering the soaring demand for plastic and rubber products, we have come up with a common platform for all plastic and rubber manufacturers, suppliers, exporters and buyers, to trade with each other at the click of a mouse. A few years back, transactions used to take place ‘on –field’, with both parties sitting face-to-face, before closing the deal. Here, the major plus point is the transaction is taking place ‘on-line’ and you can strike a profitable deal right away. Sitting face-to-face can be done anytime.

Plastic Fiber Optics

A glass or plastic fiber that diffuses light along its path is fiber optics. Light is stored in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fiber Optics is used as light guides to conduct the stream of light source to a point of use. These guides brighten parts that are too small or too harmful to fix a light bulb. The plastic light guide and the glass light guide are the two sorts of light guides.

The general common term for a wide range of synthethic or semi synthetic organic amorphous solid materials, plastic is used in the manufacture of industrial products. Plastics are typically polymers of molecular mass, and may contain other substances to improve performance and/or to reduce costs. There are different types of plastics for different uses: cellulose-based plastics, backelite, polystyrene and PVC polystyrene, nylon, and rubber plastics. These are used for molding, plastic models, plumbing, gutters, house siding, enclosures for computers and other electronic gear, among others.

In fiber optis technology, plastic is used as plastic light guides. Fiber optic light guides consist of non-coherent bundles of optical fibers. The fibers at each end of the bundle are tightly compressed, cut perpendicular to the axis of the fibers, and polished to permit light to pass into and out of the bundle. They have a bendable outer cover and a light-conducting core. So that that the ends of the fibers spread out distinctly to lighten different points from a single light source, multi-leg devices are rip along the length of the light guide. Although flexible glass fiber optics is more flexible than plastic fiber optics, the latter is more suitable for the transmission of light in the visible and near-infrared range. Furthermore, plastic light guides have hardly any luminous loss over distance and are better suited for UV light transmission.

Choosing what guides to use requires a careful study of physical and performance specifications. Physical specifications refer to length, diameter, and termination method. Keep in mind that some light guides are terminated with a threaded or unthreaded ferrule, a tube-like mechanical fixture that confines the stripped end of a fiber bundle while others are unterminated devices. However, performance specifications refer to wavelength, acceptance angle, bend angle, and numerical aperture.

Acceptance angle is the maximum angle measured from the axis within which light is accepted or given out by the light guide and transmitted along its length, and the bend radius is the smallest bend that fibers can bear prior to fracture. Numerical aperture refers to the calculated, optical value that indicated a device's ability to collect light over a range of input angles.

When you have decided which light you need, go to a trusted provider of fiber optics and related devices to ensure that your product, be it fiber optic cables or transceiver modules, pass industry standard qualifications.

Laser Cutting Companies

Since Theodore Maiman invented the first functional laser or LASER (Light Amplification by Stimulated Emission of Radiation) in 1960, this device, which generates a strong, highly concentrated beam of single-wavelength light, has found several uses in different industries and in various fields including medicine, consumer electronics and information technology.

Its most prominent industrial use is laser cutting. It is said that about $4.5 billion worth of laser cutting systems are being used around the world today. Most of them are being used in Japan.

In the U.S., the technology is also recognized for making companies in the automotive, aerospace, garment, architectural, construction and furniture manufacturing industries more competitive in terms of productivity and quality.

As laser cutting technology gets more advanced, and as its application gets more comprehensive, laser cutting companies are also offering high rates. These companies either manufacture laser cutting equipment or provide high-precision laser cutting facilities and services.

Many laser cutting service providers offer other services such as etching, slotting, plasma cutting, welding, punching forming and polishing of metals, aside from distortion-free metal cutting. Laser cutting of other materials such as wood, ceramics, plastics and rubber are also offered by these companies.

A complete laser cutting service package may cover designing of the parts, furnishing of materials, state-of-the-art laser cutting, quality control, delivery of parts and technical consulting services.

Laser cutting equipment manufacturers, on the other hand, make several kinds of lasers, ranging from flying optic lasers to hybrids lasers, Pivot-beam lasers and pulsed lasers. The flying optic laser is widely used for its inexpensive stationary tables and fast positioning speed (about 300m per minute). It is capable of cutting complex metal parts with small notches and intricate contours.

For piercing, it is best to use a pulsed laser since this type of laser produces a high amount of energy within a very short period of time. If you use a laser with a constant beam, the whole material being cut may melt.

The benefits of getting service from a reliable laser cutting company are many. The laser equipment only needs small floor space, it uses a small amount of heat so warping is avoided, it cuts with precision so you can minimize cutting wastes, laser cutting has lower risks of injury, and lasers cut fast, helping you increase production.

Plastic Contract Manufacturing

Plastic contract manufacturing is the process of manufacturing plastic products on a contract basis. There are many contract manufacturers of plastic products, rubber products and other specialty chemical products. They produce fabricated and extruded plastic products. The plastic fabrication facility of most of the plastic contract manufacturers include the latest Computerized Numerical Control (CNC) routers, mills and lathes for top quality machining of plastic parts and products. Plastic contract manufacturers handle plastic fabrication, CNC machining and CNC turning projects. They usually make plastic products from both natural and synthetic materials. Contract manufacturing of plastic provides plastic products of high abrasion resistance, high tensile strength, high tear strength and good oil resistance.

Plastic contract manufacturers usually make plastic products, components and assemblies at the lowest possible prices. They work together with their customers to determine the materials needed, time taken, design specifications, production developments and certifications required. Contract manufacturers of plastics come up with plastic products in any size, design or quantity, according to the needs of the customer. Most contract manufacturers have a full range of services for design engineering and manufacturing of plastic products.

Plastic contract manufacturing mainly focuses on the quality, repeatability and performance of plastic products. Some contract manufacturers specialize in producing the plastic components for high precision electronic and electrical products, consumer products, automobile products and parts. Many of them also manufacture the press components and precision components of other engineering plastics. Plastic contract manufacturers usually manufacture containers, jars, jigs and fixtures. Generally, contract manufactures use advanced technologies in injection blow molding and compression molding to produce high precision components for electronics and electrical plastics. The materials used in plastic contract manufacturing include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and high density polyethylene (HDPE).

Injection molding is widely used for thermoplastics. This process avoids the hardening of plastic in the machine. Injection molding helps to produce more accurate moldings having better control on the material usage. Many contract manufacturers of plastic specialize in the manufacturing dies for injection molded products such as plastic compounds, fan regulators, fan regulator switches, electrical rotary switches, fuse boxes and other special purpose machine parts.

Plastics and Plastic Manufacturing

Plastics and Rubber Products have become a common feature in homes. For that matter even Industries have fallen hook, line and sinker for the two. Two major factors like credibility and versatility have been driving their demand. Considering the soaring demand for plastic and rubber products, we have come up with a common platform for all plastic and rubber manufacturers, suppliers, exporters and buyers, to trade with each other at the click of a mouse. A few years back, transactions used to take place ‘on –field’, with both parties sitting face-to-face, before closing the deal. Here, the major plus point is the transaction is taking place ‘on-line’ and you can strike a profitable deal right away. Sitting face-to-face can be done anytime.

Many polymer-forming processes are essentially two stage; the first stage with polymers being the production of the polymer in a powder, granule or sheet form and the second stage being the shaping of this material into the required shape. The first stage can involve the mixing with the polymer of suitable additives and other polymers in order that the finished material should have the required properties. Second-stage processes for thermoplastics forming generally involve heating the powder, granule or sheet material until it softens, shaping the softened material to the required shape and then cooling it. For thermosets the second-stage processes involve forming the thermosetting materials to the required shape and then heating them so that they undergo a chemical change to cross-link polymer chains into a highly linked polymer. The main second-stage processes used for forming polymers are:

Plastics Moulding

This includes injection moulding, reaction compression moulding and transfer moulding.

Plastics Forming

This includes such processes as extrusion, plastic vacuum forming, plastic blow moulding and calendering.

Plastics Cutting

Injection moulding,

In addition, products may be formed by polymer joining. The processes are:

Adhesives, Plastic Welding,Fastening systems such as riveting, press and snap fits and screws.

The choice of process will depend on a number of factors, such as:

The quantity of items required The size of the items

The rate at which the items are to be produced, i.e. cycle time The requirements for holes, inserts, enclosed volumes, threads Whether the material is thermoplastic or thermoset

Plastic Injection moulding

Moulding uses a hollow mould to form the product. The main processes are injection moulding, reaction injection moulding, compression moulding and transfer moulding.

A widely used process for thermoplastics, though it can also used for rubbers, thermosets and composites, is injection moulding. With this process, the polymer raw material is pushed into a cylinder by a screw or plunger, heated and then pushed, i.e. injected, into the cold metal mould. The pressure on the material in the mould is maintained while it cools and sets. The mould is then opened and the component extracted, and then the entire process repeats itself. High production rates can be achieved and complex shapes with inserts, threads, holes, etc. produced; sizes range from about 10 g to 25 kg in weight. Typical products are beer or milk bottle crates, toys,

control knobs for electronic equipment, tool handles, pipe fittings.

Reaction injection moulding

Reaction injection moulding involves the reactants being combined in the mould to react and produce the polymer. The choice of materials that are processed in this way is determined by the reaction time, this must be short, e.g. 30 seconds, so that cycle times are short. It is mainly used with polyurethanes, polyamides and polypropylene oxide and composites incorporating glass fibres. The preheated reactants are injected at high speed into a closed mould where they fill the mould and

combine to produce the finished product. This method is used for large automotive parts such as spoilers, bumpers and front and rear fascia.

Compression moulding

Compression moulding is widely used for thermosets. The powdered polymer is compressed between the two parts of the mould and heated under pressure to initiate the polymerisation reaction. The process is limited to relatively simple shapes from a 2-3 g to 15 kg in weight. Typical products are dishes, handles and electrical fittings.

Transfer moulding

Transfer moulding differs from compression moulding in that the powdered polymer is heated in a chamber before being transferred by a plunger into the heated mould.

Plastic Forming processes

Forming processes involve the flow of a polymer through a die to form the required shape.

Plastic Extrusion forming

A very wide variety of plastic products are made from extruded sections, e.g. curtain rails, household guttering, window frames, polythene bags and film. Extrusion involves the forcing of the molten thermoplastic polymer through a die. The polymer is fed into a screw mechanism which takes the polymer through the heated zone and forces it out through the die. In the case of an extruded product such as curtain rail, the extruded material is just cooled.

If thin film or sheet is required, a die may be used which gives an extruded cylinder of material. This cylindrical extruded material is inflated by compressed air while still hot to give a tubular sleeve of thin film . The expansion of the material is accompanied by a reduction in thickness. Such film can readily be converted into bags.

Polyethylene is readily processed to give tubular sleeves by this method but polypropylene presents a problem in that the rate of cooling is inadequate to prevent crystallisation and so the film is opaque and rather brittle. Flat film extrusion can be produced using a slit-die. The rate of cooling, by the use of rollers, can be made fast enough to prevent crystallisation occurring with polypropylene. The extrusion process can be used with most thermoplastics and yields continuous lengths of product. Intricate shapes can be produced and a high output rate is possible.

Plastic Blow moulding

Blow moulding is a process used widely for the production of hollow articles such as plastic bottles from thermoplastics. Containers of a wide range of sizes can be produced. With extrusions blow moulding the process involves the extrusion of a hollow thick-walled tube which is then clamped in a mould. Pressure is applied to the inside of the tube to inflate it so that it fills the mould. Blow moulding can also be used with injection moulding.

Plastic vacuum forming

Vacuum forming is a common method of thermoforming. It uses a vacuum on one side of a sheet of heat-softened thermoplastic to force it against a cooled mould and hence produce the required shape. Sheets, such as 6 mm thick acrylic, are likely to be preheated in ovens before being clamped, but thinner sheets are likely to be heated by radiant heaters positioned over the mould. Vacuum forming can have a high output rate, but dimensional accuracy is not too good and such items as holes, threads and enclosed shapes cannot be produced.

Calendering

Calendering is a process used to form thermoplastic films, sheets and coated fabrics. The most common use has been for plasticised PVC. Calendering consists of feeding a heated paste-like mass of the plastic into the gap between two rolls, termed nip rolls. It is squeezed into a film which then passes over cooling rolls before being wound round a wind-up roll. This process can also be used to coat a fabric with a polymer.

Plastic machining

The processes used to shape a polymer generally produce the finished article with no further, or little, need for machining or any other process. With injection moulding, compression moulding and blow moulding there is a need to cut off gates and flashing; with extrusion, lengths have to be cut off. As with metals, single-point and multi-point cutting tools can be used with polymers. Where discontinuous, rather than continuous, chips are produced and the machined surface becomes excessively rough as a result of chips being sheared off. It is thus desirable to select cutting conditions which result in the formation of continuous chips.

Polymers tend to have low melting points and thus machining conditions which do not result in high temperatures being produced are vital if material is not to soften and deform.

Plastic Manners in a Rubber Society

I'm rubber, you're glue, whatever you say, bounces off of me and sticks to you. You've heard it said across the land. From playground to playground. The early training in speech for politely letting the aggressor know they have crossed the line. This is supposed to shock them into stopping in their tracks. The problem with this is that each generation learns less from the one before about how to use its manners. This creates a cycle of practiced pretense at having manners. People creating their own moral code. What they think good behavior should be. Everyone sets the bar at a different level. So, while little Bobby chants about rubber and glue, Bubba is making a knuckle sandwich. After all, these are the manners he is learning at home.

That is just school yard politics. Let us talk about adults on an average shopping day. The setting is a mildly warm Texas day in the end of December. Just a few days before Christmas. All the stores have the tinny music of the season blasting out of the speakers. Shoppers are wandering to and fro in a last minute shopper stupor. People are pushing and shoving. No apologies uttered. Grabbing items haphazardly from off the shelf. Change of heart, throw it on a shelf in another department. Who cares anyway, that's what the people get paid for right? Rush, get it don't make eye contact. What is the first thing you notice as you look around when you walk into a store, restaurant or coffee shop? That's right, No one wants to be there. Especially the employees. Not very often do you hear I'll be with you in a moment. It can be frustrating yes? Yes.

Another area that I notice a lack of learned politeness is when you are in the never ending loop of being passed from non-helpful person to non-helpful person on the phone with customer support. The veiled contempt that a customer is shown over the phone is very difficult to deal with. Often I feel like dispensing with good manners and having a nice verbal throw down. Especially after the 3rd or 4th person. More often than not, say with a cable company, you are told it is user error. This makes you feel quiet bright. Am I right? I think I am.

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Let's not even talk about what happens as we drive about. How about people calling to telemarket at your home? Doesn't that feel like an invasion? Not so polite. I don't mean to be so negative. It would just be so much more of a peaceful and quiet world to live in if we were all a bit more polite and nicer to one another.