Flexibility and effectiveness in injection molding technology

Fastening of tools (moulds) in injection molding machines

Changing molds in injection molding machines can be very time-consuming and costly. With quick-release devices and hot runner adapter plates, this problem can be solved and time and money saved. A&E develops these panels on a project-specific basis.

Tools (moulds) are fastened to the fixed and moving mold platens in injection molding machines with horizontally arranged shooting units. Also in injection molding machines with vertically arranged clamping units (colloquially known as vertical machines), the installation takes place between the upper and the lower mold platen.

The two halves of the mold – the ejector-side and the nozzle-side mold halves – are fastened using clamping brackets or directly with fastening screws, which firmly connect the clamping plates of the molds to the clamping plates of the injection molding machine. It is irrelevant whether the mold mounting plates of the injection molding machines have threaded holes according to EUROMAP 2 or T-slots.

With frequent changes, especially with larger tools, the installation and removal of the tools quickly becomes a not inconsiderable time and cost factor. In order to simplify and shorten the tool change, mechanical, hydraulic and electromagnetic quick-clamping devices are offered by various companies on the market.

Requirements for frequent tool changes

Hot runner adapter plate 600 x 600 x 140mm with mechanical quick clamping device

In any case, the quick-clamping devices must ensure that the mold is firmly and thus “immovably” connected to the clamping plates of the injection molding machine and that it remains in place during the opening and closing movements as well as the build-up and reduction of the closing and nozzle contact forces, the ejector , the core pull movements and movements of other tool attachments do not lead to relative movements between the tool halves and the machine plates.

With the advent of the so-called “multi-component” injection molding technologies since the 1970s – a mold has several sprue bushes for the same or different polymer melts – injection molding machines with several injection units were also developed and built. The layers/positions of the sprue bushings on the multi-component molds are determined by the molded part to be produced. The layers/positions of the injection units of the injection molding machines must then be designed in such a way that the nozzles of the injection units reach the respective sprue bushings and the melt can be injected into the mold cavities.

Best practises

If a multi-component injection mold is to be installed on a machine with a different arrangement of the injection units than originally intended, the melt connections between the nozzle of the injection unit and the mold sprue bush can be restored with hot runner adapter plates. If molds are changed frequently on machines with such hot runner adapter plates, quick-action clamping devices can also be used for these applications, as two examples below show. Such hot runner adapter plates are developed and manufactured by A&E on a project or customer basis.

Hot runner adapter plate 2,900 x 1,790 x 190mm with magnetic clamping plate, assembly situation

Using a mechanical quick release unit with a hot runner adapter plate

Exploded view of magnetic chuck, hot runner adapter plate, fixed platen of the machine (from left to right)

A DEMAG ergotech 100/420-310 injection molding machine with a vertically arranged injection unit was fitted with a hot runner adapter plate, which directs the melt from the nozzle of the vertical injection unit to the center of the machine’s fixed platen, so that injection molds with the sprue bushing arranged centrally on the nozzle side can also be used could be used on this machine. The nozzle pressure force of the hot runner to the mold sprue bushing is applied via a mechanically actuated clamping device. In order to realize quick tool changes, the tool is fastened to the hot runner adapter plate using a mechanical quick-action clamping device. The clamping force is applied via a bayonet catch between the tool and the hot runner adapter plate. When the lever on the side is actuated, the bayonet lock attached to the lever engages in the counterparts attached to the tool centering and the clamping force is applied. The bayonet lock is self-locking, the tool is securely clamped.

Hot runner adapter plate for merging the melts from two horizontally parallel injection units in connection with magnetic quick-release plates.

For injection molding machines ENGEL DUO 1700 2F and ENGEL DUO 2700, the melt streams of both injection units are brought together in a hot runner adapter plate onto a mold sprue bush – melt flow from “two to one”. If molds are installed that only need one melt flow to fill the mold parts, the hot runner in the adapter plate can be removed and replaced by a hot runner that only directs the melt flow of an injection unit to the centrally located mold sprue bush. Since both injection units are arranged symmetrically to the center of the fixed mold platen of the machine, the hot runner can connect the nozzle of one or the other injection unit with the mold sprue bush – melt flow from “one to one”. Another special feature of these hot runner adapter plates is that the nozzle contact forces of the injection units are absorbed in the adapter plate and the contact force of the hot runner nozzle is built up by spring assemblies in the adapter plate. The hot runner is mounted in the adapter plate in such a way that the hot runner nozzle can perform a stroke in order to reach different layers/positions of the mold sprue bushings in relation to the clamping level.

Magnetic quick-release plates are also provided for these hot-runner adapter plates, since frequent tool changes are planned in production. It is up to the customer whether to install the magnetic clamping plate between the tool and the hot runner adapter plate or between the hot runner adapter plate and the fixed machine plate.

In addition to a permanently effective clamping force of the quick-action clamping device or the magnetic clamping plate, it must be ensured that the invisible connection between the mold sprue bushing and the hot runner nozzle always remains free of melt leakage.

A&E Produktionstechnik GmbH offers a pneumatic leakage sensor for this. A small stream of compressed air flows continuously through a capillary located near the nozzle. If melt leakage occurs, the pressure in the capillary increases and the sensor control generates an optical and acoustic warning signal.

The hot runner adapter plates with the quick clamping devices or the magnetic clamping plates have been in production since 2017.

Airtect melt leakage sensor - view of hot runner nozzle with Airtect capillary

“When using recyclates, economic efficiency must be taken into account”

Interview with Dr.-Ing. Volker Reichert, Owner and CEO of A & E Produktionstechnik GmbH

Dr.-Ing. Volker Reichert, Owner and CEO of A & E Produktionstechnik GmbH

Can sandwich injection moulding, for which your company has developed a special nozzle, contribute to the recycling of recycled plastics?

Dr. Reichert: Sandwich injection molding is one way to reprocess recycled plastics in a meaningful way. It is not a panacea, as new plastic is also required for the production of new moulded parts and the recycled plastics must have an appropriate quality. The process always requires two melt streams consisting of different materials that means two plasticizing units. Those additional investment as well as operating costs must be taken into account in questions of cost-effectiveness.

So you can’t hide unsorted and poorly prepared recyclates in the core layer?

Dr. Reichert: If high-quality parts are produced, they need high-quality recyclates. If you pay two- or three-digit euro amounts per kilogram for high-quality engineering plastic, then you cannot fill in recyclates that may only be in the cent range. In principle, it is possible to recycle plastics from the Yellow Bag. However, the parts produced out of those materials do not meet the requirements specified on them. Under recycling or circulatory aspects, it should be the purpose to use the same materials for skin and core. So that the material properties are approximately the same. If you inject sandwich parts made of different plastics, you will later have the problem that you have to separate them during recycling.

The sandwich process has been around for decades. Will it become more important due to the current development towards more recyclate use?

Dr. Reichert: It is without a doubt, sandwich technology was always a niche process. Importance will increase due to the fact of circular requirements.  However, what kind of growth rates we may achieve is questionable.

Nevertheless, the pressure to use recyclates is increasing.

Dr. Reichert: Many of our customers, i.e. the injection moulders, do not want the OEM’s of the moulded parts to know that recyclate has been processed. At present, however, we also notice that under the keywords circular economy and resource conservation, the proportion of recyclates is certainly indicated. The problem, however, is that with recyclate processing, the injection moulder takes responsibility for ensuring that the moulded parts with recyclate also meet the specified specifications. This leads to renewed testing and certification for high-quality parts. These costs must be generated again. The mostly lower price of recyclates alone will not be sufficient in many cases.

The higher costs are increasingly offset by the ecological benefits.

Dr. Reichert: In general, anyone who uses recyclates instead of virgin material has an ecological advantage. The production of recyclate does not release as much CO2 as new material. So far, this aspect has hardly played a role, but that is changing. It is foreseeable that processors, i.e. our customers, will be legally obliged to declare the CO2 footprint for their products. Assuming that the footprint for new material is 100 and for recyclate only 50 kilograms of CO2 per plastic unit used, then the use of recyclate suddenly becomes very important. Recyclate manufacturers can already provide information on how much smaller the CO2 footprint of their products is compared to virgin material.

Reducing the CO2 footprint is one thing, but at the same time, the functionality should remain the same.

Dr. Reichert: That is the way it is. Therefore the sandwich process has quite advantages. There are now additives that even improve the mechanical properties of the recyclates. The recyclates become worse and worse in the course of repeated reprocessing because the molecular chains degrade. There are now ways to sell the recyclates in such a way that they are almost equal to new material. Such a high-quality recycled material can be perfectly used as a core layer for sandwich components.

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The world is facing major challenges: climate change must be combated, the environment must be protected and resources must be conserved. It is also important to make good use of the opportunities offered by digitization. The plastics industry has a key role in this process, because plastics are omnipresent in the world.

Climate protection, digitalization and the circular economy are therefore also the three major topics at K 2022, the world’s leading trade fair for the plastics industry. To get in the mood for the industry meeting in autumn 2022, the VDMA has representatives of plastics machinery construction and all other stakeholders in the industry have their say in weekly interviews.

 
Lüfterrad
Fig. 1: Fan runner made from PBT/PBT recyclate; Source: CKT-Ökoplast GmbH 2021

Concealed melt splices

Concealed spices (spices that are not directly visible to the machine operator or machine setter) that are used in hot runner technology always involve the risk of melt leakage. Getting these overmoulded hot runners back on track is a complex affair – dismantling, thermal and mechanical cleaning, reassembly. It is not uncommon for these cleanings to be combined with the complete replacement of the electrical resistance heating.

Since the hot runners in the A&E intermediate plates can perform a stroke in order to easily reach different depths of the tool sprue bushings, the machine setter must be particularly careful to set this connection leak-free.

An adjustable contour template is supplied to the customer as a simple aid.

This means that before the mould is installed, it can be checked whether the hot runner nozzle can safely reach the mould sprue bushing without any component collision.

In the case of hot runner and 2K sandwich intermediate plates, in which the nozzle contact pressure for the tool sprue bushing is generated in the steel plate, the exact nozzle position can be read on the nozzle adjustment device.

A&E uses a sensor from the Irish company Airtect as a further aid to avoid melt leaks at this point. This sensor consists of a capillary tube through which air flows and evaluation electronics. The capillary tube is attached in the immediate vicinity of the melt bore of the nozzle.

If melt emerges from the spice between the tool sprue and the hot runner nozzle, the pressure of the air flowing out rises in the capillary tube. This change in pressure is detected by the sensor electronics and an optical and / or acoustic signal is generated. The signal can, however, also be processed further via a corresponding interface in the machine control system, for example to trigger an alarm or an error message.

Reuse old plastics

A&E Sandwich panel

In future, plastics processors will have to use a proportion of old plastics (recyclates = regrind, re-granulates) for or in their plastic products. These are legal requirements of the EU and the federal government. A large number of measures are required in order to be able to meet these requirements. There are several technologies for reusing and recycling old plastics:

  • mechanical recycling, i. e. melt thermoplastics again and process them into new products using injection moulding and / or extrusion
  • chemical recycling, i. e. old plastics are broken down into their components (molecular chains) using chemical processes. There is a separation of “foreign components”. The molecular chains are then transformed into new plastics in further chemical processes.
  • thermal recycling, i. e. incineration, use of the heat of combustion. This technology is no longer practicable in view of climate change, as CO2 is also produced when it is burned.

Of course, it is possible to shred the old moulded parts, melt them again and immediately manufacture new moulded parts using injection moulding. This is also done on a large scale and is state of the art, but this is not so easy with all old plastics. Old plastics are mostly dirty and often consist of several different plastics. In addition, certain properties (mechanical strength values) deteriorate as a result of reprocessing.

Collecting used plastics is also problematic in plastics recycling. In order to be able to use old plastics economically, they must:

  • be pure,
  • free of impurities and foreign bodies (stones, glass, ceramics …),
  • be safely available in sufficient quantities,
  • do not have poorer properties to a large extent as a result of reprocessing.

However, the conventional waste plastics add up to millions of tons of different plastics. Various old plastics cannot be processed directly into new parts

Sandwich process: economical processing of old plastics

The sandwich process (coinjection / coinjection) offers a solution for the processing of old plastics – sandwich injection moulding, which is used for the production of moulded parts made of plastic. In the sandwich process, the old plastics are “hidden” inside the moulded part without the properties of the moulded part being impaired by the old plastic. Processing old plastics in this way is therefore one of the options for mechanical recycling.

The hot and liquid plastic is injected into a temperature-controlled mould, where it cools down and hardens. The injection moulding of thermoplastics is based on the swelling flow effect: The plastic melt flows in the mould cavity (mold-forming cavity) from the injection point to the end of the flow path through already solidified melt. This forms the surface of the moulded part (“skin”). If during the injection – while the mould is being filled – a different melt type is used, e.g. it is injected melt from recycled material, this remains in the core of the molded part, surrounded by a “skin” of e. g. new plastic.

Depending on the geometry of the moulded part and the thermoplastic types used, the process enables up to 60% of the core material, for example recycled / old plastics, to be injected into the interior of the moulded parts. The old plastic is then no longer visible (see Fig. 1 red) and the properties of these parts do not differ from those that are injection-moulded from 100% new material. Nature has a good example for this. The bones of birds, for example, consist of a compact surface (skin), but are largely hollow inside. Nature practically practiced “lightweight construction” here. The weight is reduced, unnecessary material is omitted. The mechanical loads are only transmitted through the compact skin, not through the inside. In sandwich injection molding, “superfluous” material is replaced by the old plastics.

Es wurde kein Alt-Text für dieses Bild angegeben.

Fig. 1: Sandwich injection moulding – basic process sequence (injection sequence from left to right)

Economical and environmentally friendly plastic with the sandwich process

By using old plastics, sandwich injection moulding offers an economic advantage: Recyclates are not as expensive as new material. That benefits the company. Another major advantage is the environmental aspect. In this way, old plastics are put to a new use and the environmental impact is reduced. The application of the process is not limited to new molded parts. Moulded parts that have already been produced can also be converted to production using this process. The prerequisites for sandwich injection moulding are machine and process know-how, two-component injection moulding machines and cold runner bar casting tools.

The best solution from an expert hand

A&E Produktionstechnik GmbH has been offering the corresponding nozzle technology and process know-how for both new machines and machines that are already in production. 2K sandwich units that are installed in different “housings” are part of this product family. 2K sandwich unit stands for two-component sandwich nozzles or valves with which the sandwich injection moulding process (coinjection) can be carried out on multi-component injection moulding machines. Our team of competent engineers works out economical solutions for your machine, tool and process adjustments and also puts them into operation on your machines. A&E stands for applications and developments for plastics processing and has proven high quality in production, reliability and innovation for almost two decades.

Development of innovative injection moulding technologies

Automatisierung und Entwicklung innovativer Spritzgießtechnologien aus Expertenhand
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A&E like automation and development or sales and efficiency. A&E Produktionstechnik GmbH from Dresden offers both. The Saxon company has been developing, producing and selling flexible injection solutions for single, multi-component and vertical injection moulding machines since 2002. The main focus of the development work is on increasing the efficiency and the cost-saving flexibility of single, multi-component and vertical injection moulding machines. One of the company’s most innovative technologies is the A&E sandwich panels. They enable plastics processors to convert their injection moulding machines inexpensively to the sandwich injection molding process and thus, for example, comply with the legal requirements of the EU and the federal government through the use of recyclates. The advantage: You don’t have to deal with the classic problems that arise with the legally required reuse of old plastics, e.g. the deterioration in properties through the use of old plastics. In the sandwich injection moulding process, secondary raw materials, i. e. plastics that have already been disposed of at least once are used to manufacture new products – in this case moulded parts made of plastic. Here, the old plastics are “hidden” inside the moulded part without the properties of the moulded part being impaired by the old plastic. The prerequisite is that specialists support the processing of recyclates using the sandwich method. The sandwich process is not limited to this application. For example, it is also possible to foam the core material – ideal for lightweight construction applications.

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Efficient use

The hot runner sandwich plates from A&E offer more efficiency and / or flexibility when using injection moulding machines. The principle is simple. Hot runners in intermediate plates connect the nozzles of the injection units with the mould sprue bushes if their positions are different. Due to the safe, adjustable, non-positive connection of the tool sprue bushing to the hot runner nozzle, the highest level of leakage security is offered. The hot runners are slidably mounted in the intermediate plates in order to achieve different positions of the tool sprue bushes in relation to the clamping surface. The contact force between the hot runner nozzle and the mould sprue bushing is generated via an adjusting device. The contact force to the tool sprue bushing is steplessly adjustable independently of the machine and can act permanently or cyclically.

The advantages are obvious: By using the hot runner intermediate plates, no machine and / or mould conversion is necessary if the positions / positions of the nozzles of the injection units do not match those of the moulds.

The hot runner plates can be assembled and disassembled just as easily as with conventional tool installation and removal. If service is required, the hot runner can simply be dismantled from the steel plate and serviced. This reduces downtimes and costs, even if the tool is changed frequently, and increases service life. In addition, sensors, e.g. to monitor the nozzle contact force, and the injection moulding machine can be expanded to include additional special injection moulding processes.

The adaptation to the customer machine and the production of the hot runner sandwich plates from A&E are made to order. They are therefore suitable for 1K, 2K and also for vertical machines

A team of competent engineers works out economical solutions for your machine, tool and process adjustments and also puts them into operation on your machines. A&E stands for applications and developments for plastics processing and has proven high quality in production, reliability and innovation for almost two decades. More efficiency and higher sales with the technologies from Saxony.