Out with the old, in with CO2

Materials World magazine
,
30 Apr 2017

Andreas Praller, Senior Expert in Plastics Industry, Application Technology at Linde, Germany, talks to Ellis Davies about the company’s gas injection moulding technology, PLASTINUM GIM C.

Tell me about your position at Linde.

I work at the Linde headquarters near Munich, Germany, in the application technology department. My role is to develop new gas-based technologies for the plastics processing industry, and launch new applications by supporting the local sales engineers and consulting with start ups and customers. It’s a mixed role between development and seeing the resulting products into the market.

What is gas injection moulding?

Gas injection moulding is a process whereby high-pressure nitrogen is injected into a melt to form a hollow part. First the plastic material is injected into the cavity, followed by the nitrogen at a certain point in the melt to create a hollow section or gas channel in the plastic part. This method can be used, for example, to manufacture a handle for a car or fridge with a long gas channel, or a part where the gas channel covers a smaller area of a bigger part, such as car door modules, when you require a stronger area. This is usually used for a thick plastic part or area in a bigger part that cannot be produced without the help of gas because the plastic shrinks when cooling. Nitrogen can compensate for this by providing internal pressure.

What is different about PLASTINUM GIM C?

The C stands for CO2 – we use liquid CO2 instead of the gaseous nitrogen. The problem with using nitrogen is that it has almost no cooling capacity, so does not contribute to the cooling of the plastic because of its low-density. In our process, liquid CO2 is injected at high pressure through a gas injector. The CO2 warms up and evaporates in the gas channel that is formed, changing its properties to become super critical. This means that it retains its pressure but has a higher density at the same volume. The higher density contributes to the cooling effect, as there are more molecules inside the chamber, and it also has a high specific heat capacity. In this process, liquid CO2 is injected at around 200 bars and is kept at a stable high pressure. At the end of the cycle the CO2 must be released or the part will burst. During this pressure release there is a significant cooling effect from the CO2, much higher than from nitrogen. 

How does PLASTINUM GIM C compare to water injection moulding methods?

Water injection moulding (WIM) offers a high cooling capacity because of the high specific heat capacity and density of water. The negative aspect is the moisture that can be left behind, which has to be removed, adding time to the cycle. 

The use of CO2 also cuts equipment costs, as the equipment for WIM is much more expensive and complicated. There is also a higher risk of instability, for example a breakthrough can occur in any injection moulding process when the liquid or gas bursts through the part because of an incorrect parameter. This is not a major problem with gas, but water can damage the mould. Customers like the cooling performance of water, but they dislike the method because it can cause major production problems. 

What was the process for producing refrigerator handles?

We worked on this product with a long-term customer, Engel Formenbau und Spritzguss GmbH, Germany, which produces refrigerator handles with nitrogen. The handles must have a smooth surface because they are not painted afterwards. Nitrogen was used because it provided the most constant quality and best finish. 

We offered Engel Formenbau und Spritzguss our new technology as an alternative. The biggest challenge concerning the change at the mould was the gas injector, which is the part that injects the CO2 into the mould. For nitrogen, the gas injector is very small, but the higher density of CO2 requires a larger injector for fast filling and release at the end of the cycle. Linde and its equipment partner Maximator GmbH, Germany, specialist in high-pressure equipment, have developed pressure boosting and control equipment suitable for CO2. This equipment was used at Engel Formenbau und Spritzguss for the trials because the standard equipment used was not suitable for CO2.

Is the process in commercial use?

It is in use at Engel Formenbau und Spritzguss, and with other customers, such as automotive suppliers of various parts. We have customers in both Europe and the USA.

Any other noteworthy projects?

We are also in the process of commercialising a spot cooling technology called PLASTINUM Temp S, another CO2 technology. This process can supplement the existing cooling phase of injection moulding. Products are usually cooled using water channels, but there can be very narrow areas in the mould where there is not enough space for these channels. With CO2, you can cool even very small areas of the mould with capillary tubes, which we work with the customers to install. By using this highly efficient cooling method, long cycle times caused by the hot spots can be reduced by up to 50% in special cases.

New hot runner solutions from HRSFlow

HRSFlow, India, has launched three new hot runner solutions that it claims optimise the injection moulding process. The company has added three new components – a three-layer tip, a pressure block and a thread safe kit – that are designed to improve the quality of the finished part. 

The pressure block is positioned between the hot runner system and the mould to increase clamp plate stiffness and provide an optimal thermal profile. Made with low heat conductible materials, it allows flexible positioning that does not negatively affect the thermal profile of the system. 

The company says that the optimisation of the injection moulding process is key to the production of a quality finished part, but the simplification of routine maintenance is also an important consideration. The thread safe kit is intended to achieve this by providing easy nozzle removal without thread damage. 

Greener records

Dutch CD manufacturer Symcon has received an EU grant to develop an injection moulding technology that could create vinyl records at a lower cost by reducing the energy required by up to 65%. The process injects plastic into the record’s grooves, copying the grooves on the stamper accurately. 

Conventional record printing requires a large amount of steam to heat the PVC before it is pressed into shape with stampers, whereas injection moulding puts no strain on the stampers, making them last longer. Instead of using steam, the plastic is heated in advance and injected into the mould. This allows for a lower energy input and less waste material. The method is also said to be quicker, with records turned around in two weeks as opposed to the standard 12–16. 

The moulded records are currently not as durable as the stamped vinyl, however, and are slightly more expensive to produce. Symcon is looking to improve on this to make the process commercially viable, bringing the costs down to below current levels. 

Collaborative overmoulding project underway 

Combining press forming and injection moulding, the ThermoPlastic composites Research Centre, Netherlands, has closed a two-year collaborative deal with an array of European injection moulding companies for the overmoulding of thermoplastic composites with the design and manufacture of an advanced demonstrator part. 

The part is designed for the aerospace sector, and is a grid stiffened panel combining stiffness and strength with dimensional accuracy. It is made of TenCate Cetex TC1225 composite and overmoulded with Victrex PEEK90HMF40.

Faster prototyping for packaging

To reduce cost, lead-time and to improve speed-to-market capability, Plastic Technologies Inc (PTI) has added a new injection moulding technology for the prototyping and sampling of preforms. The technology has been designed to allow for quicker package validation testing and small test market distribution before a wider product launch.

PTI’s new solution allows for small quantity production for the testing of new packaging concepts. This will cut down on preforms needing to be disposed of due to over-produced prototype products. 

Denroy invests in the cloud

UK-based plastic injection moulding and tooling manufacturer the Denroy Group has invested in a cloud-based software package from Infor, USA. The investment was made to help Denroy enhance planning, service and quality control. 

The software, Infor CloudSuite Industrial, is a fully integrated, cloud-based industry specific solution suite, allowing users to manage value chains, product launches, cycle times and product configurations. The system will be used primarily by Denroy’s aerospace business because of the complexity of manufacture. 

KraussMaffei launches the LRX series

German injection moulding solutions company KraussMaffei has introduced its LRX series featuring the LRX 50, 100 and 150. The linear robots offer a flexible solution for standard injection moulding processes, covering clamping forces ranging between 350–6,500kN. 

The LRX series is for use in conjunction with all types of injection moulding machines, and can be used with a machine by any brand or manufacturer. They are compatible with KraussMaffei’s WizardX online programming software, which can be used alongside its MC6 control system.

KraussMaffei says that the series provides a cost-effective entry level solution able to deal with complex requirements. The LRXs also offer flexible gripper solution, quick demoulding times and turnkey automation cells.