Injection moulding UK spelling , or Injection molding U. 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 a helical shaped screw , and injected into a mould cavity , where it cools and hardens to the configuration of the cavity. Injection moulding is widely used for manufacturing 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.
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Silicone rubber is an elastomer rubber-like material composed of silicone —itself a polymer —containing silicon together with carbon , hydrogen , and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations.
Silicone rubbers are often one- or two-part polymers, and may contain fillers to improve properties or reduce cost. Due to these properties and its ease of manufacturing and shaping, silicone rubber can be found in a wide variety of products, including: voltage line insulators, automotive applications; cooking, baking, and food storage products; apparel such as undergarments, sportswear, and footwear; electronics; medical devices and implants; and in home repair and hardware with products such as silicone sealants.
In its uncured state, silicone rubber is a highly-adhesive gel or liquid. In order to convert to a solid, it must be cured , vulcanized , or catalyzed.
This is normally carried out in a two-stage process at the point of manufacture into the desired shape, and then in a prolonged post-cure process. It can also be injection molded. Silicone rubber may be cured by a platinum -catalyzed cure system, a condensation cure system, a peroxide cure system, or an oxime cure system. For the platinum-catalyzed cure system, the curing process can be accelerated by adding heat or pressure. In a platinum-based silicone cure system, also called an addition system because the key reaction-building polymer is an Addition reaction , a hydride - and a vinyl -functional siloxane polymer react in the presence of a platinum complex catalyst, creating an ethyl bridge between the two .
The reaction has no byproducts. Such silicone rubbers cure quickly, though the rate of or even ability to cure is easily inhibited in the presence of elemental tin , sulfur , and many amine compounds.
Condensation curing systems can be one-part or two-part systems. The silanol condenses further with another hydrolyzable group on the polymer or cross-linker and continues until the system is fully cured.
Such a system will cure on its own at room temperature and unlike the platinum-based addition cure system is not easily inhibited by contact with other chemicals, though the process may be affected by contact with some plastics or metals and may not take place at all if placed in contact with already-cured silicone compounds. The crosslinkers used in condensation cure systems are typically alkoxy, acetoxy, ester, enoxy or oxime silanes such as methyl trimethoxy silane for alkoxy-curing systems and methyl triacetoxysilane for acetoxy-curing systems.
In many cases an additional condensation catalyst is added to fully cure the RTV system and achieve a tack-free surface. Organotitanate catalysts such as tetraalkoxy titanates or chelated titanates are used in alkoxy-cured systems. Acetoxy tin condensation is one of the oldest cure chemistries used for curing silicone rubber, and is the one used in household bathroom caulk. Depending on the type of detached molecule, it is possible to classify silicone systems as acidic, neutral or alkaline.
Two-part condensation systems package the cross-linker and condensation catalyst together in one part while the polymer and any fillers or pigments are in the second part. Mixing of the two parts causes the curing to take place. Once fully cured, condensation systems are effective as sealants and caulks in plumbing and building construction and as molds for casting polyurethane, epoxy and polyester resins, waxes, gypsum, and low-melting-temperature metals such as lead.
They are typically very flexible and have a high tear strength. They do not require the use of a release agent since silicones have non-stick properties. Peroxide curing is widely used for curing silicone rubber. The curing process leaves behind byproducts, which can be an issue in food contact and medical applications. However, these products are usually treated in a postcure oven which greatly reduces the peroxide breakdown product content.
One of the two main organic peroxides used, dicumyl peroxide compare cumene hydroperoxide , has principal breakdown products of acetophenone and phenylpropanol. The other is dichlorobenzoyl peroxide, whose principal breakdown products are dichlorobenzoic acid and dichlorobenzene. The first silicone elastomers were developed in the search for better insulating materials for electric motors and generators.
Resin-impregnated glass fibers were the state-of-the-art materials at the time. The glass was very heat resistant, but the phenolic resins would not withstand the higher temperatures that were being encountered in new smaller electric motors. Chemists at Corning Glass and General Electric were investigating heat-resistant materials for use as resinous binders when they synthesized the first silicone polymers, demonstrated that they worked well and found a route to produce them commercially.
The term "silicone" is actually a misnomer. The suffix -one is used by chemists to denote a substance with a double-bonded atom of oxygen in its backbone. When first discovered, silicone was erroneously believed to have oxygen atoms bonded in this way. Technically correct term for the various silicone rubbers is polysiloxanes or polydimethylsiloxanes. Corning Glass in a joint venture with Dow Chemical formed Dow Corning in to produce this new class of materials.
As the unique properties of the new silicone products were studied in more detail, their potential for broader usage was envisioned, and GE opened its own plant to produce silicones in now Momentive Performance Materials.
Wacker Chemie also started production of silicones in Europe in The Japanese company Shin-Etsu Chemical began mass production of silicone in The companies mentioned above are now still the main competitors in the oligopoly that comprises the silicone industry.
Silicone rubber has low tensile strength, poor wear and tear wear properties. Silicone rubber is a material of choice in industry when retention of initial shape and mechanical strength are desired under heavy thermal stress or sub-zero temperatures. This makes silicone rubber one of the elastomers of choice in many extreme environments. Silicone rubber is highly inert and does not react with most chemicals. Due to its inertness, it is used in many medical applications including medical implants.
It is biocompatible , hypoallergenic , which makes it suitable for baby care products, and food contact in general. Silicone rubber is a reliable solution as opposed to rubber and thermoplastic elastomers for migration or interaction problems between the main active ingredients.
Its chemical stability prevents it from affecting any substrate it is in contact with skin, water, blood, active ingredients, etc. To make silicone, the silicon atoms must be isolated from the silicon dioxide compound silica. From here, there are several processes where silicon is combined with methyl chloride and heated. It is then distilled into a polymerised siloxane known as polydimethylsiloxane.
The polydimethylsiloxane can then be polymerised. This is done using a variety of techniques depending on the use of the final product. Curing is the final stage in the production process. Polysiloxanes differ from other polymers in that their backbones consist of Si—O—Si units unlike many other polymers that contain carbon backbones. Polysiloxane is very flexible due to large bond angles and bond lengths when compared to those found in more basic polymers such as polyethylene.
For example, a C—C backbone unit has a bond length of 1. The siloxane backbone differs greatly from the basic polyethylene backbone, yielding a much more flexible polymer. Because the bond lengths are longer, they can move farther and change conformation easily, making for a flexible material. Polysiloxanes also tend to be chemically inert, due to the strength of the silicon-oxygen bond.
Despite silicon being a congener of carbon, silicon analogues of carbonaceous compounds generally exhibit different properties, due to the differences in electronic structure and electronegativity between the two elements; the silicon-oxygen bond in polysiloxanes is significantly more stable than the carbon-oxygen bond in polyoxymethylene a structurally similar polymer due to its higher bond energy also because polyoxymethylene decomposes formaldehyde, which is volatile and escapes driving decomposition forward, but Si-containing decomposition products of silicone are less volatile.
A variety of fillers can be used in silicone rubber, although most are non-reinforcing and lower the tensile strength. Silicone rubber is available in a range of hardness levels, expressed as Shore A or IRHD between 10 and , the higher number being the harder compound.
It is also available in virtually any colour, and can be colour matched. Once mixed and coloured, silicone rubber can be extruded into tubes, strips, solid cord or custom profiles according to the size specifications of the manufacturer. Cord can be joined to make O-rings and extruded profiles can be joined to make seals. Silicone rubber can be moulded into custom shapes and designs. Manufacturers work to set industry tolerances when extruding, cutting or joining silicone rubber profiles.
Silicone rubber is used in automotive applications, many cooking, baking, and food storage products, apparel including undergarments, sportswear, and footwear, electronics, to home repair and hardware, and a host of unseen applications. Liquid silicone rubber is also manufactured for life science applications syringe pistons, closure for dispensing system, gaskets for IV flow regulator, respiratory masks, implantable chambers for IV administration , cosmetic products Mascara brush, make-up packaging, make-up applicator and lipstick moulds and optics products circular lens, collimators , Fresnel lenses and free form lenses.
Its property of not having a carbon backbone, but a chemically robust silicon backbone instead, reduces its potential as a food source for dangerous waterborne bacteria such as Legionella. Non-dyed silicone rubber tape with an iron III oxide additive making the tape a red-orange colour is used extensively in aviation and aerospace wiring applications as a splice or wrapping tape due to its non-flammable nature.
The iron oxide additive adds high thermal conductivity but does not change the high electrical insulation property of the silicone rubber.
This type of self-amalgamating tape amalgamates or fuses to itself, so that when stretched and wrapped around cables, electrical joints, hoses and pipes it bonds into a strong seamless rubbery electrically insulating and waterproof layer, although not adhesive.
With the addition of carbon or another conductive substance as a powdered filler, silicone rubber can be made electrically conductive while retaining most of its other mechanical properties.
As such it is used for flexible contacts which close on being pressed, used in many devices such as computer keyboards and remote control handsets. In , silicone rubber formed the matrix of the first autonomic self-healing elastomer. Additionally, this material had improved fatigue properties as evaluated using a torsion-fatigue test. From Wikipedia, the free encyclopedia. Chem Soc. Pharmaceutical Polymers Smithers Rapra.
L and Pizzi, A. Retrieved Viking Extrusions". Foam rubber Micronized rubber powder Cold rubber. Polymer additive Plasticizer Polymer stabilizers Biodegradable additives Filler materials.
Rubber tapping Rubber technology Vulcanization. Rubber pollution Great Pacific garbage patch Persistent organic pollutant Dioxins Environmental hazards Tire-derived fuel Rubber recycling Airfield rubber removal.
Polymax [ citation needed ].
Most of the rubber made parts change in physical properties during storage and ultimately become unserviceable, for example, leads to excessive hardening, softening, cracking, crazing, or other surface degradation. These changes may be the result of one particular factor or a combination of factors, such as the action of oxygen, ozone, light, heat, humidity or oils and solvents. The deleterious effects of these factors may, however, be minimized by careful choice of storage conditions. The effects of low temperature are not permanently deleterious to rubber articles by they may become stiffer if stored at low temperatures and care should be taken to avoid distoting them during handling at that temperature.
Shelf Life of Rubber Products
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Safe Storage of Rubber Products
The Library Life of a rubber mold is the length of time a rubber mold will remain useful after being placed in storage. When properly taken care of, molds can have a library life of up to 10 years or more. Avoid tin-cured condensation-cure silicone rubbers as they only last two to four years depending on conditions. Also avoid Poly-Fast , a polyurethane rubber that degrades quickly in storage.
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There are three basic methods that can be employed to mold rubber products; compression, transfer and injection. Choosing the right method depends on several factors. UniRubber will select the correct method to meet your individual needs. The purpose of this section is to list some of the factors affecting tolerances. In general, the degree of reproducibility of dimensions depends upon the type of tooling and rubber used, and the state of the art. Discussion of Factors Affecting Tolerances. There are many factors involved in the manufacturing of molded rubber products which affect tolerances. Since these may be peculiar to the rubber industry, they are listed here. Shrinkage is defined as the difference between corresponding linear dimensions of the mold and of the molded part, both measurements being made at room temperature. All rubber materials exhibit some amount of shrinkage after molding when the part cools.
Extruded and Molded Rubber Products
Rubber products can remain in inventory for long periods of time. Shelf life, the storage period prior to part installation, varies by elastomer type. Storage conditions such as temperature, humidity, ozone, and exposure to light also affect the shelf life of rubber products. By understanding these factors and best practices, buyers can make informed decisions about sourcing elastomers and storing die cut seals, gaskets, and O-rings. Environmental conditions such as high temperatures and high humidity can cause unwanted physical changes in rubber products. For best results, ARP recommends storing rubber parts according to the following guidelines. For organizations that source elastomeric materials and store die cut rubber products, the following table contains shelf life recommendations by elastomer type. Buyers can use this information to make sourcing decisions that account for the time a batch of rubber has been inventory, and the expected length of time that die cut rubber parts will be stored.
Molded Rubber Products
It is very important for the user to know, the material properties and expected shelf-life of rubber products in storage can be adversely affected by the following:. Likewise, Rubber products should not be stored near sources of heat, such radiators and base heaters. Rubber products should not be stored under conditions of high or low humidity. Certain compounds of rubber are susceptible to mold degradation.
Factors Affecting Tolerances in Molded Rubber Parts
Silicone rubber is an elastomer rubber-like material composed of silicone —itself a polymer —containing silicon together with carbon , hydrogen , and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers are often one- or two-part polymers, and may contain fillers to improve properties or reduce cost. Due to these properties and its ease of manufacturing and shaping, silicone rubber can be found in a wide variety of products, including: voltage line insulators, automotive applications; cooking, baking, and food storage products; apparel such as undergarments, sportswear, and footwear; electronics; medical devices and implants; and in home repair and hardware with products such as silicone sealants.
How close to the end of the expiration date of the shelf life can rubber products be used? It depends on the storage conditions, which can affect the quality and shelf life of rubber products.
It features a low viscosity for easy mixing and pouring and cures with minimal bubble entrapment. Mix ratio is 1A:1B by volume 85AB by weight , pot life is 25 minutes and the rubber cures with an ultimate Shore hardness of Shore 45A. Cured rubber is dimensionally stable low shrinkage , offers good wear resistance and excellent library life. They are not compatible and inhibition will result.