Misplaced Pages

#563436

107-495: POM is characterized by its high strength, hardness and rigidity to −40 °C. POM is intrinsically opaque white because of its high crystalline composition but can be produced in a variety of colors. POM has a density of 1.410–1.420   g/cm. Typical applications for injection-molded POM include high-performance engineering components such as small gear wheels, eyeglass frames , ball bearings , ski bindings , fasteners, gun parts, knife handles, and lock systems. The material

214-408: A $ 2.7 billion deal, Hoechst Celanese sold its Trevira division to a consortium between Houston -based KoSa, a joint venture of Koch Industries , IMASAB S.A., and Grupo Xtra , both of Mexico. Also in 1998, Hoechst combined most of its industrial chemical operations into a new company, Celanese AG. In 1999, Hoechst spun off Celanese AG as a publicly traded German corporation, cross-listed on both

321-520: A $ 2.9 billion profit. In June 2009, the company sold its polyvinyl alcohol (PVOH) business to Sekisui Chemical Co., Ltd . Celanese has a process to make ethanol from natural gas . In late 2020, Celanese sold their 45% stake in Polyplastics to Daicel , who already owned 55% of the company. This transaction resulted in Daicel attaining full ownership of Polyplastics. In 1985, Hoechst Celanese

428-506: A $ 20 million plant in Rock Hill, South Carolina , to produce polybenzimidazole (PBI), a material used to fabricate high-performance protective apparel used in firefighter's gear and astronaut space suits . Celanese spun off its pharmaceutical business as Celgene in 1986. In 1987, Celanese Corporation was acquired by Hoechst and merged with its American subsidiary, American Hoechst, to form Hoechst Celanese Corporation. In 1998, in

535-634: A 20th-century American architect , to build the “ Celanese House ,” a model home in New Canaan, Connecticut , to showcase the company's new materials and styles. Celanese bought operations of the British chemicals firm Imperial Chemical Industries in 1982. This included the Fiber Industries Incorporated plant in Salisbury, North Carolina , a part of Invista since 2004. In 1983, Celanese built

642-404: A cavity perpendicular to the draw direction, to form overhanging part features. When the mould is opened, the slides are pulled away from the plastic part by using stationary “angle pins” on the stationary mould half. These pins enter a slot in the slides and cause the slides to move backward when the moving half of the mould opens. The part is then ejected and the mould closes. The closing action of

749-566: A different colour, is injection-moulded into those spaces. Pushbuttons and keys , for instance, made by this process have markings that cannot wear off, and remain legible with heavy use. Manufacturers go to great lengths to protect custom moulds due to their high average costs. The perfect temperature and humidity level is maintained to ensure the longest possible lifespan for each custom mould. Custom moulds, such as those used for rubber injection moulding, are stored in temperature and humidity controlled environments to prevent warping. Tool steel

856-421: A helical screw), and injected into a mould cavity , where it cools and hardens to the configuration of the cavity. After a product is designed, usually by an industrial designer or an engineer , moulds are made by a mould-maker (or toolmaker) from metal , usually either steel or aluminium , and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing

963-435: A high-grade stainless steel may be a more appropriate choice. In addition, POM can have undesirable characteristics when burned. The flame is not self-extinguishing, shows little to no smoke, and the blue flame can be almost invisible in ambient light. Burning also releases formaldehyde gas, which irritates nose, throat, and eye tissues. Injection molding Injection moulding (U.S. spelling: injection molding )

1070-467: A hopper into a heated barrel with a reciprocating screw. Upon entrance to the barrel, the temperature increases and the Van der Waals forces that resist relative flow of individual chains are weakened as a result of increased space between molecules at higher thermal energy states. This process reduces its viscosity , which enables the polymer to flow with the driving force of the injection unit. The screw delivers

1177-433: A large variation in dimensions from cycle-to-cycle. More commonly used now is scientific or decoupled moulding, a method pioneered by RJG Inc. In this the injection of the plastic is "decoupled" into stages to allow better control of part dimensions and more cycle-to-cycle (commonly called shot-to-shot in the industry) consistency. First the cavity is filled to approximately 98% full using velocity (speed) control. Although

SECTION 10

#1732899086564

1284-598: A lifetime of 50 years service. According to the lawsuit, scientists from the defendants allegedly reported that the PB plumbing systems would degrade even when exposed to low concentrations of chlorine typically found in municipal water systems. The lawsuit claimed that in spite of this knowledge, the defendants concealed the information and continued to market these products (Shell supplying PB resins to water pipe manufacturers and Hoechst Celanese providing acetal resins to manufacturers of pipe fittings) until approximately 1996. The lawsuit

1391-492: A material hopper, an injection ram or screw-type plunger, and a heating unit. Also known as platens, they hold the moulds in which the components are shaped. Presses are rated by tonnage, which expresses the amount of clamping force that the machine can exert. This force keeps the mould closed during the injection process. Tonnage can vary from less than 5 tons to over 9,000 tons, with the higher figures used in comparatively few manufacturing operations. The total clamp force needed

1498-554: A new plastic layer to form around the first part. This is often referred to as overmoulding. This system can allow for production of one-piece tires and wheels. Moulds for highly precise and extremely small parts from micro injection molding requires extra care in the design stage, as material resins react differently compared to their full-sized counterparts where they must quickly fill these incredibly small spaces, which puts them under intense shear strains. Two-shot, double-shot or multi-shot moulds are designed to "overmould" within

1605-415: A number of illnesses. Hoechst Celanese asked the courts to dismiss these charges as spurious, claiming that its discharges have not caused substantial harm to anyone or to the environment, and further asserting that a 3-year limit on tort claims had expired, relieving the company of any responsibility for damages which might be eventually discovered. Acetyl intermediates is Celanese's largest segment, with

1712-428: A patented process for treating acetal homopolymer called satinizing that creates a surface roughness sufficient for micromechanical interlocking. There are also processes involving oxygen plasma and corona discharge. In order to get a high bond strength without specialized tools, treatments, or roughening, one can use Loctite 401 prism adhesive combined with Loctite 770 prism primer to get bond strengths of ~1700psi. Once

1819-517: A plant to produce its own version of acetal resin, named Delrin , at Parkersburg, United States . Also in 1960, Celanese completed its own research. Shortly thereafter, in a limited partnership with the Frankfurt firm Hoechst AG , a factory was built in Kelsterbach , Hessen ; from there, Celcon was produced starting in 1962, with Hostaform joining it a year later. Both remain in production under

1926-511: A product range consisting of basic chemicals such as acetic acid , acetic anhydride , and vinyl acetate . Customers of acetyl intermediates and industrial specialties are in the chemical, paint and coatings, construction, and adhesive industries for polymerization . Advanced engineered materials offers plastic polymers to customers in the automotive, electronics, telecommunications, and medical industries. Major products include engineered plastics for fuel system components (provided by Ticona ,

2033-404: A single moulding cycle and must be processed on specialised injection moulding machines with two or more injection units. This process is actually an injection moulding process performed twice and therefore can allow only for a much smaller margin of error. In the first step, the base colour material is moulded into a basic shape, which contains spaces for the second shot. Then the second material,

2140-767: A slurry) or in neat trioxane (e.g. in an extruder). After polymerization, the acidic catalyst must be deactivated and the polymer stabilized by melt or solution hydrolysis to remove unstable end groups. Stable polymer is melt-compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers. POM is supplied in a granulated form and can be formed into the desired shape by applying heat and pressure. The two most common forming methods employed are injection molding and extrusion . Rotational molding and blow molding are also possible. Typical applications for injection-molded POM include high-performance engineering components (e.g. gear wheels, ski bindings, yoyos , fasteners, lock systems). The material

2247-410: A small shot weight and fills gradually until the mould is 95 to 99% full. Once they achieve this, they apply a small amount of holding pressure and increase holding time until gate freeze off (solidification time) has occurred. Gate freeze off time can be determined by increasing the hold time, and then weighing the part. When the weight of the part does not change, the gate has frozen and no more material

SECTION 20

#1732899086564

2354-422: A solidified thermoset component. After the part has solidified, valves close to isolate the injection system and chemical precursors , and the mould opens to eject the moulded parts. Then, the mould closes and the process repeats. Pre-moulded or machined components can be inserted into the cavity while the mould is open, allowing the material injected in the next cycle to form and solidify around them. This process

2461-418: A timely manner, chemical crosslinking may occur causing the screw and check valves to seize and potentially damaging the injection moulding machine. Injection moulding consists of the high pressure injection of the raw material into a mould, which shapes the polymer into the desired form. Moulds can be of a single cavity or multiple cavities. In multiple cavity moulds, each cavity can be identical and form

2568-470: A variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower-temperature thermoplastics, can be used for some simple injection moulds. Injection moulding uses a special-purpose machine that has three parts: the injection unit, the mould and the clamp. Parts to be injection-moulded must be very carefully designed to facilitate

2675-476: Is 38–45 on the Rockwell-C scale . Hardened steel moulds are heat treated after machining; these are by far superior in terms of wear resistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C (HRC). Aluminium moulds can cost substantially less, and when designed and machined with modern computerised equipment can be economical for moulding tens or even hundreds of thousands of parts. Beryllium copper

2782-406: Is a manufacturing process for producing parts by injecting molten material into a mould, or mold . Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses , elastomers , confections , and most commonly thermoplastic and thermosetting polymers. Material for the part is fed into a heated barrel, mixed (using

2889-469: Is a function of the resin being used, and can be relatively predictable. To prevent spikes in pressure, the process normally uses a transfer position corresponding to a 95–98% full cavity where the screw shifts from a constant velocity to a constant pressure control. Often injection times are well under 1 second. Once the screw reaches the transfer position the packing pressure is applied, which completes mould filling and compensates for thermal shrinkage, which

2996-580: Is a relatively strong plastic, nearly as strong as epoxy, or aluminum, but a bit more flexible:   POM is wear-resistant: POM materials can have trademarked producer-specific names, for example "Delrin". Prices for large quantities, in October 2023, in US$ /kg: Prices and availability retail / small wholesale : Retail price November 2023 in the Netherlands ;: from 19 to 27 euro/dm3 POM

3103-406: Is a strong and hard plastic, about as strong as plastics can be, and therefore competes with e.g. epoxy resins and polycarbonates . The price of POM is about the same as that of epoxy. There are two main differences between POM and epoxy resins: while POM can be cast when melted and adheres to practically nothing. Epoxy resins are often used with glass fiber reinforcement, but for POM that

3210-450: Is also susceptible to alkaline attack and is more susceptible to degradation in hot water. Thus low levels of chlorine in potable water supplies (1–3 ppm) can be sufficient to cause environmental stress cracking , a problem experienced in both the US and Europe in domestic and commercial water supply systems. Defective mouldings are most sensitive to cracking, but normal mouldings can succumb if

3317-622: Is also the world's largest producer of vinyl acetate monomer (VAM). Celanese operates 25 production plants and six research centers in 11 countries, mainly in North America, Europe, and Asia. The company owns and operates the world's three largest acetic acid plants: one in the Clear Lake area of Pasadena , Texas , one on Jurong Island in Singapore , and a third in Nanjing , China . In 1918,

Polyoxymethylene - Misplaced Pages Continue

3424-412: Is dealt with in the next section.}) Some extremely high production volume moulds (like those for bottle caps) can have over 128 cavities. In some cases, multiple cavity tooling moulds a series of different parts in the same tool. Some toolmakers call these moulds family moulds, as all the parts are related—e.g., plastic model kits. Some moulds allow previously moulded parts to be reinserted to allow

3531-452: Is determined by the projected area of the part being moulded. This projected area is multiplied by a clamp force of from 1.8 to 7.2 tons for each square centimetre of the projected areas. As a rule of thumb, 4 or 5 tons/in can be used for most products. If the plastic material is very stiff, it requires more injection pressure to fill the mould, and thus more clamp tonnage to hold the mould closed. The required force can also be determined by

3638-401: Is immersed in paraffin oil (kerosene). A voltage applied between tool and mould causes spark erosion of the mould surface in the inverse shape of the electrode. The number of cavities incorporated into a mould directly correlate in moulding costs. Fewer cavities require far less tooling work, so limiting the number of cavities lowers initial manufacturing costs to build an injection mould. As

3745-443: Is injected into the part. Gate solidification time is important, as this determines cycle time and the quality and consistency of the product, which itself is an important issue in the economics of the production process. Holding pressure is increased until the parts are free of sinks and part weight has been achieved. Injection moulding is a complex technology with possible production problems. They can be caused either by defects in

3852-424: Is known as insert moulding and allows single parts to contain multiple materials. This process is often used to create plastic parts with protruding metal screws so they can be fastened and unfastened repeatedly. This technique can also be used for In-mould labelling and film lids may also be attached to moulded plastic containers. A parting line , sprue , gate marks, and ejector pin marks are usually present on

3959-430: Is maintained to compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mould opens and the part is ejected. Traditionally, the injection portion of the moulding process was done at one constant pressure to fill and pack the cavity. This method, however, allowed for

4066-451: Is not an option because it does not adhere to the glass fibres. Epoxy resins needs time to cure, while POM has fully matured as soon as it has cooled down. POM has very little shrinkage: from 165 °C to 20 °C it shrinks by just 0.17%. When supplied as extruded bar or sheet, POM may be machined using traditional methods such as turning, milling, drilling etc. These techniques are best employed where production economics do not merit

4173-428: Is often used. Mild steel, aluminium, nickel or epoxy are suitable only for prototype or very short production runs. Modern hard aluminium (7075 and 2024 alloys) with proper mould design, can easily make moulds capable of 100,000 or more part life with proper mould maintenance. Moulds are built through two main methods: standard machining and EDM . Standard machining, in its conventional form, has historically been

4280-726: Is one of the world's largest producers of cellulose acetate . Acetate products are primarily used in cigarette filters , as well as in the production of fashion apparel and linings . Celanese also manufactures Clarifoil cellulose acetate film that is wood pulp based and certified biodegradable and compostable in home and industrial composting conditions. Industrial specialties, using the feedstock from acetyl intermediates, manufactures polymer and emulsions such as polyvinyl acetate emulsions, and specialty chemicals as ethylene vinyl acetate . Major end-use markets include polyvinyl alcohol producers, paper, mortar and gypsum, textiles, paints, coatings, and adhesives manufacturers. TCX Technology

4387-417: Is quite high for thermoplastics relative to many other materials. The packing pressure is applied until the gate (cavity entrance) solidifies. Due to its small size, the gate is normally the first place to solidify through its entire thickness. Once the gate solidifies, no more material can enter the cavity; accordingly, the screw reciprocates and acquires material for the next cycle while the material within

Polyoxymethylene - Misplaced Pages Continue

4494-449: Is repeated. For a two-shot mould, two separate materials are incorporated into one part. This type of injection moulding is used to add a soft touch to knobs, to give a product multiple colours, or to produce a part with multiple performance characteristics. For thermosets, typically two different chemical components are injected into the barrel. These components immediately begin irreversible chemical reactions that eventually crosslinks

4601-417: Is the most common modern method of manufacturing plastic parts; it is ideal for producing high volumes of the same object. Injection moulding uses a ram or screw-type plunger to force molten plastic or rubber material into a mould cavity; this solidifies into a shape that has conformed to the contour of the mould. It is most commonly used to process both thermoplastic and thermosetting polymers , with

4708-409: Is typically dioxolane , but ethylene oxide can also be used. Dioxolane is formed by reaction of ethylene glycol with aqueous formaldehyde over an acid catalyst. Other diols can also be used. Trioxane and dioxolane are polymerized using an acid catalyst, often boron trifluoride etherate , BF 3 OEt 2 . The polymerization can take place in a non-polar solvent (in which case the polymer forms as

4815-427: Is typically very difficult to bond, with the copolymer typically responding worse to conventional adhesives than the homopolymer. Special processes and treatments have been developed to improve bonding. Typically these processes involve surface etching, flame treatment , using a specific primer/adhesive system, or mechanical abrasion. Typical etching processes involve chromic acid at elevated temperatures. DuPont uses

4922-423: Is used in areas of the mould that require fast heat removal or areas that see the most shear heat generated. The moulds can be manufactured either by CNC machining or by using electrical discharge machining processes. The mould consists of two primary components, the injection mould (A plate) and the ejector mould (B plate). These components are also referred to as moulder and mouldmaker . Plastic resin enters

5029-402: Is used to fill the mould cavity, compensate for shrinkage, and provide a cushion (approximately 10% of the total shot volume, which remains in the barrel and prevents the screw from bottoming out) to transfer pressure from the screw to the mould cavity. When enough material has gathered, the material is forced at high pressure and velocity into the part forming cavity. The exact amount of shrinkage

5136-536: Is widely used in the automotive and consumer electronics industry. POM's electrical resistivity is 14×10 Ω⋅cm making it a dielectric with a 19.5 MV/m breakdown voltage. Polyoxymethylene was discovered by Hermann Staudinger , a German chemist who received the 1953 Nobel Prize in Chemistry . He had studied the polymerization and structure of POM in the 1920s while researching macromolecules , which he characterized as polymers. Due to problems with thermostability , POM

5243-489: Is widely used in the automotive and consumer electronics industry. There are special grades that offer higher mechanical toughness, stiffness or low-friction/wear properties. POM is commonly extruded as continuous lengths of round or rectangular section. These sections can be cut to length and sold as bar or sheet stock for machining. POM is a hard plastic, that cannot be glued, but can be joined to POM by melting. Melted POM does not adhere to steel tools used to shape it. POM

5350-515: The Frankfurt and New York stock exchanges as "CZZ" and "CZ", respectively. On 16 December 2003, the U.S. private equity firm Blackstone Group announced a takeover offer for Celanese, after two years of wooing management. Shareholders formally approved the offer from Blackstone on 16 June 2004, and Blackstone completed the acquisition of Celanese AG. The company was delisted from the New York Stock Exchange , and Blackstone changed

5457-482: The 1940s because World War II created a huge demand for inexpensive, mass-produced products. In 1946, American inventor James Watson Hendry built the first screw injection machine, which allowed much more precise control over the speed of injection and the quality of articles produced. This machine also allowed material to be mixed before injection, so that coloured or recycled plastic could be added to virgin material and mixed thoroughly before being injected. In

SECTION 50

#1732899086564

5564-495: The 1970s, Hendry went on to develop the first gas-assisted injection moulding process, which permitted the production of complex, hollow articles that cooled quickly. This greatly improved design flexibility as well as the strength and finish of manufactured parts while reducing production time, cost, weight and waste. By 1979, plastic production overtook steel production, and by 1990, aluminium moulds were widely used in injection moulding. Today, screw injection machines account for

5671-572: The American Cellulose & Chemical Manufacturing Company (known as Amcelle) was founded in New York City by Swiss chemist Camille Dreyfus . The American Cellulose and Chemical Manufacturing Co. Ltd plant in Cumberland, Maryland , was set up during World War I to produce cheaper fabric for airplane manufacturing. The plant location was chosen inland to protect against Zeppelin attacks. It

5778-400: The article using pins, sleeves, strippers, etc., may cause undesirable impressions or distortion, so care must be taken when designing the mould. The standard method of cooling is passing a coolant (usually water) through a series of holes drilled through the mould plates and connected by hoses to form a continuous pathway. The coolant absorbs heat from the mould (which has absorbed heat from

5885-415: The auspices of Celanese and are sold as parts of a product group now called 'Hostaform/Celcon POM . Different manufacturing processes are used to produce the homopolymer and copolymer versions of POM. To make polyoxymethylene homopolymer , anhydrous formaldehyde must be generated. The principal method is by reaction of the aqueous formaldehyde with an alcohol to create a hemiformal , dehydration of

5992-419: The chemical precursors are minimised in the injection unit. The residence time can be reduced by minimising the barrel's volume capacity and by maximising the cycle times. These factors have led to the use of a thermally isolated, cold injection unit that injects the reacting chemicals into a thermally isolated hot mould, which increases the rate of chemical reactions and results in shorter time required to achieve

6099-453: The conventional process description above, there are several important moulding variations including, but not limited to: A more comprehensive list of injection moulding processes may be found here: [1] Like all industrial processes, injection molding can produce flawed parts, even in toys. In the field of injection moulding, troubleshooting is often performed by examining defective parts for specific defects and addressing these defects with

6206-410: The core and cavity of moulds further influences cost. Rubber injection moulding process produces a high yield of durable products, making it the most efficient and cost-effective method of moulding. Consistent vulcanisation processes involving precise temperature control significantly reduces all waste material. Usually, the plastic materials are formed in the shape of pellets or granules and sent from

6313-451: The cost of design, fabrication , processing , and quality monitoring. The skillful mould and part designer positions these aesthetic detriments in hidden areas if feasible. In 1846 the British inventor Charles Hancock, a relative of Thomas Hancock , patented an injection molding machine. American inventor John Wesley Hyatt , together with his brother Isaiah, patented one of the first injection moulding machines in 1872. This machine

6420-435: The design of the mould or the characteristics of the process itself. Trials are often performed before full production runs in an effort to predict defects and determine the appropriate specifications to use in the injection process. When filling a new or unfamiliar mould for the first time, where shot size for that mould is unknown, a technician/tool setter may perform a trial run before a full production run. They start with

6527-424: The direction that the mould opens, unless parts of the mould are designed to move from between such overhangs when the mould opens using components called Lifters. Sides of the part that appear parallel with the direction of draw (the axis of the cored position (hole) or insert is parallel to the up and down movement of the mould as it opens and closes) are typically angled slightly, called draft, to ease release of

SECTION 60

#1732899086564

6634-676: The engineering polymer business of Celanese), conveyor belts, electronics, safety systems, emissions filtration, and fluid handling. Polymer production is improved by the acquisition of SO.F.TER Group, Forlì , in Italy in 2016. The food ingredients business Nutrinova produces the high intensity sweetener Sunett ( acesulfame K ), the preservatives Nutrinova, potassium sorbate , and sorbic acid , and other food ingredients. Major end-use markets include beverages, confections, baked goods, and dairy products. In 2021, Celanese ranked 7th on FoodTalks' Global Top 20 Food Preservative Companies list. Celanese

6741-542: The entity's name back to Celanese Corporation. Under Blackstone, a number of streamlining initiatives were undertaken, and several acquisitions were made. On 21 January 2005, Celanese Corporation conducted an initial public offering and became a publicly traded corporation traded on the New York Stock Exchange under the symbol "CE". When Blackstone sold the last of its shares in 2007, it had made five times what it had invested and it, and its co-investors collected

6848-438: The expense of melt processing. The material is free-cutting, but does require sharp tools with a high clearance angle. The use of soluble cutting lubricant is not necessary, but is recommended. POM sheets can be cut cleanly and accurately using an infrared laser, such as in a CO 2 laser cutter . Because the material lacks the rigidity of most metals, care should be taken to use light clamping forces and sufficient support for

6955-406: The final part. None of these features are typically desired, but are unavoidable due to the nature of the process. Gate marks occur at the gate that joins the melt-delivery channels (sprue and runner) to the part forming cavity. Parting line and ejector pin marks result from minute misalignments, wear, gaseous vents, clearances for adjacent parts in relative motion, and/or dimensional differences of

7062-407: The first soluble forms of cellulose acetate in 1903, which was much less flammable than cellulose nitrate . It was eventually made available in a powder form from which it was readily injection moulded. Arthur Eichengrün developed the first injection moulding press in 1919. In 1939, Arthur Eichengrün patented the injection moulding of plasticised cellulose acetate. The industry expanded rapidly in

7169-476: The hemiformal/water mixture (either by extraction or vacuum distillation ) and release of the formaldehyde by heating the hemiformal. The formaldehyde is then polymerized by anionic catalysis , and the resulting polymer stabilized by reaction with acetic anhydride . Due to the manufacturing process, large-diameter cross-sections may have pronounced centerline porosity. A typical example is DuPont's Delrin. The polyoxymethylene copolymer replaces about 1–1.5% of

7276-493: The hot plastic) and keeps the mould at a proper temperature to solidify the plastic at the most efficient rate. To ease maintenance and venting, cavities and cores are divided into pieces, called inserts , and sub-assemblies, also called inserts , blocks , or chase blocks . By substituting interchangeable inserts, one mould may make several variations of the same part. More complex parts are formed using more complex moulds. These may have sections called slides, that move into

7383-404: The injection and clamping cycles; however, aluminium moulds are cost-effective in low-volume applications, as mould fabrication costs and time are considerably reduced. Many steel moulds are designed to process well over a million parts during their lifetime and can cost hundreds of thousands of dollars to fabricate. When thermoplastics are moulded, typically pelletised raw material is fed through

7490-411: The material into a single connected network of molecules. As the chemical reaction occurs, the two fluid components permanently transform into a viscoelastic solid. Solidification in the injection barrel and screw can be problematic and have financial repercussions; therefore, minimising the thermoset curing within the barrel is vital. This typically means that the residence time and temperature of

7597-488: The material used and the size of the part. Larger parts require higher clamping force. Mould or die are the common terms used to describe the tool used to produce plastic parts in moulding. Since moulds have been expensive to manufacture, they were usually only used in mass production where thousands of parts were being produced. Typical moulds are constructed from hardened steel , pre-hardened steel, aluminium, and/or beryllium-copper alloy. The choice of material for

7704-548: The melting surfaces contacting the injected polymer. Dimensional differences can be attributed to non-uniform, pressure-induced deformation during injection, machining tolerances , and non-uniform thermal expansion and contraction of mould components, which experience rapid cycling during the injection, packing, cooling, and ejection phases of the process. Mould components are often designed with materials of various coefficients of thermal expansion. These factors cannot be simultaneously accounted for without astronomical increases in

7811-407: The method of building injection moulds. With technological developments, CNC machining became the predominant means of making more complex moulds with more accurate mould details in less time than traditional methods. The electrical discharge machining (EDM) or spark erosion process has become widely used in mould making. As well as allowing the formation of shapes that are difficult to machine,

7918-412: The mold is not only based on cost considerations, but also has a lot to do with the product life cycle . In general, steel moulds cost more to construct, but their longer lifespan offsets the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel moulds are less wear-resistant and are used for lower volume requirements or larger components; their typical steel hardness

8025-493: The mould causes the slides to move forward along the angle pins. A mould can produce several copies of the same parts in a single "shot". The number of "impressions" in the mould of that part is often incorrectly referred to as cavitation. A tool with one impression is often called a single impression (cavity) mould. A mould with two or more cavities of the same parts is usually called a multiple impression (cavity) mould. (Not to be confused with "Multi- shot moulding" {which

8132-399: The mould cavity through a gate and runner system. The mould remains cold so the plastic solidifies almost as soon as the mould is filled. The sequence of events during the injection mould of a plastic part is called the injection moulding cycle. The cycle begins when the mould closes, followed by the injection of the polymer into the mould cavity. Once the cavity is filled, a holding pressure

8239-404: The mould cools so that it can be ejected and be dimensionally stable. This cooling duration is dramatically reduced by the use of cooling lines circulating water or oil from an external temperature controller. Once the required temperature has been achieved, the mould opens and an array of pins, sleeves, strippers, etc. are driven forward to demould the article. Then, the mould closes and the process

8346-522: The mould through a sprue or gate in the injection mould; the sprue bushing is to seal tightly against the nozzle of the injection barrel of the moulding machine and to allow molten plastic to flow from the barrel into the mould, also known as the cavity. The sprue bushing directs the molten plastic to the cavity images through channels that are machined into the faces of the A and B plates. These channels allow plastic to run along them, so they are referred to as runners. The molten plastic flows through

8453-674: The moulding process; the material used for the part, the desired shape and features of the part, the material of the mould, and the properties of the moulding machine must all be taken into account. The versatility of injection moulding is facilitated by this breadth of design considerations and possibilities. Injection moulding is used to create many things such as wire spools , packaging , bottle caps , automotive parts and components, toys, pocket combs , some musical instruments (and parts of them), one-piece chairs and small tables, storage containers, mechanical parts (including gears), and most other plastic products available today. Injection moulding

8560-492: The moulds, or more often by the moulding process itself. Celanese Celanese Corporation , formerly known as Hoechst Celanese , is an American technology and specialty materials company headquartered in Irving , Texas . It is a Fortune 500 corporation. The company is the world's leading producer of acetic acid , producing about 1.95 million tonnes per year, representing approximately 25% of global production. Celanese

8667-427: The number of cavities play a vital role in moulding costs, so does the complexity of the part's design. Complexity can be incorporated into many factors such as surface finishing, tolerance requirements, internal or external threads, fine detailing or the number of undercuts that may be incorporated. Further details, such as undercuts, or any feature that needs additional tooling, increases mould cost. Surface finish of

8774-426: The part from the mould. Insufficient draft can cause deformation or damage. The draft required for mould release is primarily dependent on the depth of the cavity; the deeper the cavity, the more draft necessary. Shrinkage must also be taken into account when determining the draft required. If the skin is too thin, then the moulded part tends to shrink onto the cores that form while cooling and cling to those cores, or

8881-408: The part may warp, twist, blister or crack when the cavity is pulled away. A mould is usually designed so that the moulded part reliably remains on the ejector (B) side of the mould when it opens, and draws the runner and the sprue out of the (A) side along with the parts. The part then falls freely when ejected from the (B) side. Tunnel gates, also known as submarine or mould gates, are located below

8988-415: The parting line or mould surface. An opening is machined into the surface of the mould on the parting line. The moulded part is cut (by the mould) from the runner system on ejection from the mould. Ejector pins, also known as knockout pins, are circular pins placed in either half of the mould (usually the ejector half), which push the finished moulded product, or runner system out of a mould. The ejection of

9095-440: The polymer is sensitive to both chlorine and acid hydrolysis, it may perform very poorly when exposed to the reactive gases, particularly hydrogen chloride ( HCl ). Failures in this latter instance can occur with seemingly unimportant exposures from well sealed joints and do so without warning and rapidly (the component will split or fall apart). This can be a significant health hazard, as the glass may open or smash. Here, PTFE or

9202-465: The preparation of high-molecular-weight hemiacetal -terminated (~O−CH 2 OH) POM, but these lack sufficient thermal stability to be commercially viable. The inventor of a heat-stable (and therefore useful) POM homopolymer was Stephen Dal Nogare, who discovered that reacting the hemiacetal ends with acetic anhydride converts the readily depolymerizable hemiacetal into a thermally stable, melt-processable plastic. In 1960, DuPont completed construction of

9309-486: The pressure should be sufficient to allow for the desired speed, pressure limitations during this stage are undesirable. Once the cavity is 98% full, the machine switches from velocity control to pressure control , where the cavity is "packed out" at a constant pressure, where sufficient velocity to reach desired pressures is required. This lets workers control part dimensions to within thousandths of an inch or better. Although most injection moulding processes are covered by

9416-420: The process allows pre-hardened moulds to be shaped so that no heat treatment is required. Changes to a hardened mould by conventional drilling and milling normally require annealing to soften the mould, followed by heat treatment to harden it again. EDM is a simple process in which a shaped electrode, usually made of copper or graphite, is very slowly lowered onto the mould surface over a period of many hours, which

9523-412: The raw material forward, mixes and homogenises the thermal and viscous distributions of the polymer, and reduces the required heating time by mechanically shearing the material and adding a significant amount of frictional heating to the polymer. The material feeds forward through a check valve and collects at the front of the screw into a volume known as a shot . A shot is the volume of material that

9630-409: The raw material manufacturers in paper bags. With injection moulding, pre-dried granular plastic is fed by a forced ram from a hopper into a heated barrel. As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted. As the plunger advances, the melted plastic is forced through a nozzle that rests against the mould, allowing it to enter

9737-409: The runner and enters one or more specialised gates and into the cavity geometry to form the desired part. The amount of resin required to fill the sprue, runner and cavities of a mould comprises a "shot". Trapped air in the mould can escape through air vents that are ground into the parting line of the mould, or around ejector pins and slides that are slightly smaller than the holes retaining them. If

9844-441: The same parts or can be unique and form multiple different geometries during a single cycle. Moulds are generally made from tool steels , but stainless steels and aluminium moulds are suitable for certain applications. Aluminium moulds are typically ill-suited for high volume production or parts with narrow dimensional tolerances, as they have inferior mechanical properties and are more prone to wear, damage, and deformation during

9951-803: The strength and function required for the final part, as well as the cost, but also each material has different parameters for moulding that must be taken into account. Other considerations when choosing an injection moulding material include flexural modulus of elasticity, or the degree to which a material can be bent without damage, as well as heat deflection and water absorption. Common polymers like epoxy and phenolic are examples of thermosetting plastics while nylon , polyethylene , and polystyrene are thermoplastic. Until comparatively recently, plastic springs were not possible, but advances in polymer properties make them now quite practical. Applications include buckles for anchoring and disconnecting outdoor-equipment webbing. Injection moulding machines consist of

10058-660: The surface is prepared, a number of adhesives can be used for bonding. These include epoxies , polyurethanes , and cyanoacrylates . Epoxies have shown 150–1,050 psi (1,000–7,200 kPa) shear strength. Cyanoacrylates are useful for bonding to metal, leather, rubber, cotton, and other plastics. Solvent welding is typically unsuccessful on acetal polymers, due to the excellent solvent resistance of acetal. Thermal welding through various methods has been used successfully on both homopolymer and copolymer. Acetal resins are sensitive to acid hydrolysis and oxidation by agents such as mineral acid and chlorine . POM homopolymer

10165-410: The total number of available materials for injection moulding has increased at a rate of 750 per year; there were approximately 18,000 materials available when that trend began. Available materials include alloys or blends of previously developed materials, so product designers can choose the material with the best set of properties from a vast selection. Major criteria for selection of a material are

10272-415: The trapped air is not allowed to escape, it is compressed by the pressure of the incoming material and squeezed into the corners of the cavity, where it prevents filling and can also cause other defects. The air can even become so compressed that it ignites and burns the surrounding plastic material. To allow for removal of the moulded part from the mould, the mould features must not overhang one another in

10379-458: The vast majority of all injection machines. The plastic injection moulding industry has evolved over the years from producing combs and buttons to producing a vast array of products for many industries including automotive, medical, aerospace, consumer products, toys, plumbing , packaging, and construction. Most polymers, sometimes referred to as resins, may be used, including all thermoplastics, some thermosets, and some elastomers. Since 1995,

10486-420: The volume used of the former being considerably higher. Thermoplastics are prevalent due to characteristics that make them highly suitable for injection moulding, such as ease of recycling, versatility for a wide variety of applications, and ability to soften and flow on heating. Thermoplastics also have an element of safety over thermosets; if a thermosetting polymer is not ejected from the injection barrel in

10593-428: The water is hot. Both POM homopolymer and copolymer are stabilized to mitigate these types of degradation. In chemistry applications, although the polymer is often suitable for the majority of glassware work, it can succumb to catastrophic failure. An example of this would be using the polymer clips on hot areas of the glassware (such as a flask-to-column, column-to-head or head-to-condenser joint during distillation). As

10700-588: The word “Celanese,” a combination of “cellulose” and “ease” in 1925, seeking to promote the ease of cleaning and care of their acetate yarn, or artificial silk, fabrics. They officially took this name in 1927, becoming Celanese Corporation of America. In 1947, Celanese started producing acetate fiber at its plant near Ocotlán, Jalisco, Mexico . The plant was closed in 2019. By 1958, Celanese had 13 domestic plants, three research and development centers, some 30 groups of products, and approximately 13,000 employees. In 1959, Celanese commissioned Edward Durell Stone ,

10807-492: The work piece. As can be the case with many polymers, machined POM can be dimensionally unstable, especially with parts that have large variations in wall thicknesses. It is recommended that such features be "designed-out" e.g. by adding fillets or strengthening ribs. Annealing of pre-machined parts before final finishing is an alternative. A rule of thumb is that in general, small components machined in POM suffer from less warping. POM

10914-515: The −CH 2 O− groups with −CH 2 CH 2 O−. To make polyoxymethylene copolymer , formaldehyde is generally converted to trioxane (specifically 1,3,5-trioxane , also known as trioxin). This is done by acid catalysis (either sulfuric acid or acidic ion-exchange resins ) followed by purification of the trioxane by distillation and/or extraction to remove water and other active hydrogen-containing impurities. Typical copolymers are Hostaform from Celanese and Ultraform from BASF . The co-monomer

11021-487: Was also situated in proximity to a ready source of water at the Potomac River and easy access to coal supplies and railroad lines. After a series of delays, production began on Christmas Day, 1924 with a series of cellulose acetate commercial fabrics and yarns intended as alternatives to silk . The plant was closed in 1983, and was later torn down to provide a space for a new state prison. The company had introduced

11128-436: Was named along with Shell Oil and US Brass as a defendant in a class action lawsuit for $ 7 billion in both past and potential future damages for which they were accused of being liable because of leaks in their polybutylene (PB) plumbing systems. The lawsuit alleged a complex scheme to mislead buyers into believing that PB plumbing systems were suitable for use as potable water distribution systems and purportedly enjoying

11235-401: Was not commercialized at that time. Circa 1952, research chemists at DuPont synthesized a version of POM, and in 1956 the company filed for patent protection of the homopolymer , forgetting to mention in the patent the term copolymer , opening thus the road to competitors. DuPont credits R. N. MacDonald as the inventor of high-molecular-weight POM. Patents by MacDonald and coworkers describe

11342-466: Was relatively simple compared to machines in use today: it worked like a large hypodermic needle , using a plunger to inject plastic through a heated cylinder into a mould. The industry progressed slowly over the years, producing products such as collar stays , buttons, and hair combs(generally though, plastics, in its modern definition, are a more recent development c.  1950s ). The German chemists Arthur Eichengrün and Theodore Becker invented

11449-583: Was settled in 1995 for US$ 950,000,000. In January 2014, a class action lawsuit was filed on behalf of the citizens of Cannon's Campground, seeking relief from health and environmental dangers posed by groundwater and surface water contamination emanating from the Hoechst-Celanese manufacturing plant in Spartanburg, South Carolina . The lawsuit alleged the dumping of a number of toxic chemicals into local waters, which has diminished property values and caused

#563436