Melt flow index testers come in all shapes and sizes, from completely manual machines to largely automatic solutions. Here we look at the main benefits of combining manual and automatic features within the same plastic melt flow index tester solution.

What is a melt flow index tester?

A melt flow tester measures a polymer’s ability to flow under pressure in a molten state. This is known as melt flow index (MFI) or melt flow rate (MFR) and is key to determining the processability of thermoplastics.

The MFR is also an important quality control parameter. For example, the MFR of a virgin resin can be affected by transport, storage, or processing, which may indicate degradation.

Melt flow rate testing can also help research and development departments predict how a new plastic material will behave during processing.

Different test methods are used to measure the MFR, in line with ISO 1133:2011 (A and B) and ASTM D 1238:2013 (A, B, C, and D).

Types of melt flow index testing machines

Melt flow testers can vary from simple, single-weight devices to more advanced multi-weight machines.

A manual machine means that most operations are carried out manually, from weight lifting through to calculating and recording the measurements. An automatic solution performs most operations automatically. In most cases, a combination of manual and automatic features is the recommended choice.

Melt flow testing equipment can be entirely pneumatic, motorized (electronic), or a combination of the two.

Manual vs automatic, motorized vs pneumatic

Automatic features can go a long way towards simplifying many lab operations. However, there are applications where the human factor is critical, which calls for a semi-automatic approach.

Choosing between pneumatic and motorized solutions is another key consideration. Pneumatic solutions depend on a reliable supply of compressed air, which requires adequate storage facilities and inevitably entails additional operational and maintenance costs. Motorized melt flow testers eliminate these costs.

Here are some key components that deserve special attention when choosing between manual and automatic.

Weight lifter

The weight lifter is a key component of a melt flow tester. Some motorized versions are designed to rotate automatically at the end of each test. This could be a handy feature, however, it may also generate strong vibrations that can lead to faults or affect test repeatability. By contrast, motorized weight lifters that are rotated manually, such as those developed by Instron, are less likely to encounter this kind of problem.

Compacting and purging apparatus

Pre-compacting and purging are essential components of the melt flow testing process.

Some melt flow index testing equipment has integrated, automatic compacting and purging devices while others require an external, manual pneumatic attachment. The latter tends to be less ergonomic and prone to faults. For example, the attachment may get stuck inside the barrel during purging.

But the main difference between automatic and manual purging devices relates to their impact on test repeatability. An automatic solution controlled by a load cell, where the load is entirely programmable, is more precise and less likely to affect test results.

Mass selector

An integrated melt flow tester mass selector is an important component to look out for. It enables you to choose the desired mass effortlessly, without having to physically handle heavy weights. Some of the latest versions are semi-automatic, meaning masses can be selected by operating a knob or with a touch screen interface.

Another advantage of using a selector is that masses don’t need to be loaded manually each time, speeding up the test setup process.

Whether you decide to opt for a manual or semi-automatic solution, remember that ASTM D1238 specifically requires the use of dead weights. Instron’s latest semi-automatic solutions combine load cells and dead weights and are therefore fully compliant. Other machines use load cells instead of dead weights meaning they fail to comply with ASTM D1238.

The benefits of a semi-automatic approach

The deployment of a fully automated solution is often limited to specific applications where the same test (e.g. same temperature, same material) is repeated multiple times throughout the day.

In most cases, different materials undergo different tests under different conditions, which entails changing frequently from one test setup to another. In this scenario, the human factor is key to maintaining high throughput and repeatability and calls for a semi-automatic solution. This is where software comes in.

Software: a key component of semi-automatic melt flow testing 

The latest software is designed to operate as an “app on the machine” enabling a fast test setup via an intuitive touch screen. Advanced algorithms automatically select the correct test method based on the preliminary parameters entered by the operator.

There are multiple options to easily verify and analyze test results directly via the touch screen interface. If needed, the data can also be exported to a computer for further analysis.

A semi-automatic solution that combines manual, automatic, and motorized features with the latest software is key to increasing throughput and repeatability.

You can learn more about the Instron Melt Flow Index Tester range here.