Moulded parts KNOWLEDGE & INTERESTING FACTS
The whole world of moulded and injection-moulded parts
The whole world of moulded and injection-moulded parts
Moulded and injection-moulded parts are extremely versatile and therefore difficult to catalogue: They differ in shape, dimensions, material, quantity and function. An incredible number of product developers and engineers have designed an incredible number of moulded parts. The wealth of invention knows almost no bounds.
Simply put, KREMER produces the injection moulded part you need for your purpose. We advise you on production technology, moulding and materials and do everything we can to ensure that you get exactly the part you need to make your product work perfectly. In over 50 years of company history, we have amassed a great deal of knowledge, some of which we are happy to make available to you in our collection of knowledge on moulded and injection-moulded parts. Here you will find all the important facts about materials, storage, production and disposal.
Storage and shelf life
The storage life of injection moulded rubber and elastomer parts is significantly influenced by the storage environment. Experience shows that the properties of moulded rubber parts remain virtually unchanged for several years, provided they are stored or handled properly.
CR: | 4 years |
NBR: | 4 years |
EPDM: | 6 years |
FKM: | 10 years |
FFPM/FFKM: | 10 years |
MVQ: | 10 years |
PAHs - hopefully not literally on everyone's lips
Polycyclic aromatic hydrocarbons, also known as PAHs, are a group of chemical benzene compounds. They are tiny solid particles that are present in many variations of crude oil in nature, with a proportion of approx. 0.2 to approx. 7%. As a result of petroleum refining, they are also found in important formulation components of rubber compounds such as plasticisers and industrial carbon blacks and subsequently also in seals. Specific PAH types are classified by the European Union as carcinogenic, mutagenic or toxic to reproduction. Once released into the environment, they accumulate indefinitely in soil, plants and the air and degrade only poorly. Care must therefore be taken to minimise the use of chemicals containing PAHs.
PAH-free injection moulded parts are those with an analytically determined PAH concentration of <0.2 mg/kg. Concentrations of <10 mg/kg are considered low-PAH injection moulded parts.
For moulded parts that come into direct, prolonged or repeated contact with the skin or oral cavity for a short time during normal or reasonably foreseeable use, an EU regulation has been in force since 2015 that stipulates a limit value of 1 mg/kg for eight defined PAHs.
For injection-moulded rubber parts that come into contact with food, for example, this means that the formulation, which may consist of 10-15 components, must be revised and substances containing PAHs must be replaced with alternatives.
As it is often not possible to do without carbon blacks in elastomer compounds due to their properties, low-PAH carbon blacks from special manufacturing methods must be used.
Further information on storage and shelf life
A cool, dry, moderately ventilated and dust-free storage area is essential for a long shelf life. The injection moulded parts should be stored in a temperature range between +5 and +20°C.
Cardboard packaging with inner bags or polythene bags is ideal. Protect injection moulded parts in closed cardboard boxes from daylight and ozone.
Gummi-Spritzgussteile can change their physical properties under unfavourable storage conditions. Various influencing factors such as daylight or ozone can lead to cracks, excessive weight can lead to permanent deformation or even severe hardening, which severely impairs the functionality of the seals and means that they can no longer be used.
Further information on the storage, maintenance and cleaning of rubber products can be found in DIN 7716.
Compliance with legal regulations on environmental and health protection
At KREMER, we take environmental protection and the safety of both our own employees and our customers very seriously. Compliance with the legal regulations that are imposed on us during production is a matter of course for us.
Further information on silicone
Not only can different processes be used to manufacture injection moulded parts from silicone, but also different silicone rubbers. In addition to the polymer structure, the viscosity of the material is often used as a characteristic for classification, so that a distinction is generally made between solid and liquid silicone rubber. Solid silicone is referred to as HTV silicone ("High Temperature Vulcanised"), while liquid silicone is known as LSR silicone (Liquid Silicone Rubber).
The higher price of silicone is offset by its excellent properties.
In terms of price, silicone is significantly more expensive as a material than EPDM or PVC, for example, but moulded and injection-moulded parts and other products made from it are characterised by numerous positive material properties, for example:
- Excellent high temperature resistance (up to max. +280°C)
- Excellent low-temperature flexibility (down to max. -80°C)
- Minor changes to the material properties in a wide temperature application range
- High resistance to UV radiation, chemicals, oxygen, ozone and weather influences
- hydrophobic surface
- freely colourable
Silicone rubbers are not purely organic compounds. Unlike organic rubbers with their carbon polymer chain, the polymer chain of non-crosslinked silicone consists of alternating silicon and oxygen atoms. In addition to this siloxane structure, an organic residue, usually methyl groups, is also bonded to the silicon. As silicon atoms have four bonding partners, silicone rubber is also abbreviated with a Q, which stands for "quaternary group", for example in MQ, VMQ, PVMQ or FVMQ. The properties of silicone rubber depend on the organic residue and the polymer structure. However, the material advantages clearly outweigh the disadvantages, as the silicon-oxygen chain (Si-O), at 451 kJ/mol, has a significantly higher bonding energy compared to the carbon chain (C-C) at 352 kJ/mol, with equally high chain mobility.
Crosslinkers are required to obtain a mechanically stable polymer. Platinum catalyser systems or peroxides are usually used here. The elastic network of the silicone is reinforced by fillers such as precipitated or fumed silicas. The addition of quartz ensures increased media resistance of the polymer. Otherwise, silicone requires very few additives. Their use is limited, for example, to stabilisers to optimise the material properties in special applications and to mastication aids or colours. It should be noted that some additives already have their own colour. Anti-ageing agents, plasticisers or cross-linking accelerators and retarders, on the other hand, are not required.
Compared to other elastomers, liquid silicone in particular has an extremely high purity and is odourless and tasteless. This makes the material ideal for use in the medical and food sectors.
To obtain an elastomeric material, uncrosslinked silicone rubber must first be crosslinked. Crosslinking can take place in two different ways, namely by platinum-catalysed, so-called addition crosslinking, or by peroxide crosslinking.
In addition crosslinking, the platinum catalyst is used to add the Si-H groups to the double bonds of the vinyl groups of the polymer, forming a three-dimensional network. This type of crosslinking is particularly suitable for moulded parts where odour and taste neutrality are important, such as in food applications. No decomposition products are formed during the addition crosslinking process that have any negative effect on the odour.
Another advantage of this method is the high curing speed, which can be controlled via the temperature. The time advantage is particularly useful in the production of thin-walled silicone injection moulded parts. In addition, silicone injection moulded parts can be easily demoulded and have a dry surface. This also enables simple further processing and finishing of the moulded parts and overall shorter cycle times in the production process. Addition curing is one of the most modern curing methods and is mostly used for liquid silicones.
Peroxide crosslinking is a conventional method of crosslinking using organic peroxides that has been tried and tested for decades. At elevated temperatures, the peroxides decompose into highly reactive radicals, which initiate the chemical crosslinking of the polymer chains. Oxygen contact should be avoided at all costs during peroxide crosslinking, because if the surfaces of the moulded parts come into contact with atmospheric oxygen during crosslinking, they remain sticky.
HTV silicone is a high-temperature curing solid silicone that can be supplied in various forms. It is generally a plastically mouldable, pasty and sticky material that is still just flowable and contains highly dispersed silica in addition to organic peroxides as curing catalysts. The possible delivery forms of solid silicone range from strips, profiled tapes and round cords to blocks.
As far as the tools used to produce moulded and injection-moulded parts made of high-temperature cured silicone are concerned, they are not too different in design from those used to process those made of rubber.
Oxygen contact causes sticky spots on the product surface when the material is cross-linked and also contaminates the mould. In order to prevent air inclusions, special attention must therefore be paid to optimising the venting of the mould. Mould production for solid silicone products is very favourable compared to LSR products. The advantage here is that projects with low mould costs can be produced in small quantities. For very large quantities, on the other hand, liquid silicone and very expensive and complex moulds are used.
Liquid silicones, LSR for short, consist of two components and are cross-linked by addition cross-linking. The two components are mixed in the injection unit in a ratio of 1:1 during injection moulding.
Uncured LSR is usually milky white or transparent and can be coloured just as easily as solid silicone. Apart from the considerably lower viscosity in the raw state, there are hardly any differences between liquid silicone and solid silicone in terms of electrical and mechanical properties, for example.
Injection moulded parts made from LSR are just as temperature-resistant, flexible at low temperatures and resistant to ageing as those made from high-temperature cured silicone, but they have a high elongation at break and improved tear resistance. The liquid silicone is injected into the hot mould during injection moulding, whereby low injection pressures are possible - not least in order to avoid any air inclusions. The mould design criteria are the same for liquid and solid silicone.
Compared to other silicone rubbers, the price per kilo of LSR is significantly higher, but very short cycle times and the use of a material-saving and cycle time-reducing cold runner system compensate for this. The use of a material-saving and cycle time-reducing cold runner system is therefore worthwhile. Due to their high physiological compatibility, injection moulded parts made of liquid silicone are ideal for applications with food contact.