As you can imagine, measuring the thickness of a compressible material is complicated and if done incorrectly will generate inaccurate readings.
This is something you must be aware of when working in engineering, packaging or textile industries. This is because materials such as foam, rubber or cardboard are very common across these industries. Furthermore, failing to take compression into consideration could mean the material your working with is thicker than you might think.
Okay, so what should you know when measuring compressible materials? In this article, I will discuss with you some of the main points in detail.
1. What are Compressible Materials?
Compressible materials are materials that change shape under pressure. This includes materials such as foam, leather, cloth, rubber, plastic, cardboard and even some soft wood.
Be careful not to assume that materials of the same type will begin to compress under the same amount of pressure or by the same amount, slight differences in density or hardness can make a big difference. Take for example foam; the denser it is the more pressure is needed to compress it.
The good news is that there are standards to help you choose the best instrument for your readings. In the next section, we will discuss the types of standards for the compressible material in question.
2. Standards of Measuring
Firstly, let’s clarify what I mean by standards.
In this instance, a standard is the method used to measure a material. For example, a standard may need you to use a specific type of anvil and weight when taking a measurement so that a specific pressure is applied to the material.
To this end, there are many International and National Standards that define the standard practice for measuring specific types of material. Plastic, paper, board, tissue and even textile all have their own standards which will need you to measure the material in a certain way.
These largely focus on establishing a standard set of parameters, meaning a specific material can be measured in the same way by different operators in different industries. This eliminates any difference in readings that may have been caused by different methods of measurement.
List of Standards
Here some common standards used:
- Plastic Film– BS 2782-6, DIN 53370, ISO 4593, ASTM D6988
- Paper & Board – ISO 534, ISO 3034, DIN 53105, BS EN 20534, BS 4817, TAPPI T411, SCAN P7, SCAN P31, FEFCO No 3
- Tissue– ISO 12625, BS 7387, SCAN P47
- Textile– ISO 5084e
Meeting the Standards in Practice
Fundamentally, in this instance, standardising measurement techniques means controlling the contact area and force that is exerted on the sample by the measuring device.
The contact area is determined by the size of the anvils in the measuring device. The force is normally generated either by a spring or by a specified weight.
3. How to Use Your Gauge To Meet the Compressible Material Standards
Gauges come in varying degrees of sophistication, including fully automated gauges, bench mounted and hand held gauges. Automated in-line gauges are generally designed for use on a production line, and as the name suggests, aren’t operated manually.
Bench Mounted and Hand Held gauges operate similar to each other. You would normally move a lever to raise the measuring anvil which allows you to insert your material and then release the lever to drop the anvil and take your measurement. In some cases this may work in reverse. For example moving the lever to drop the anvil, and then release to raise it.
Bench thickness gauges are very simple to use and due to the nature of their design, achieve a high level of repeatability between different operators (Reproducability).
Applying the Correct Pressure
When measuring compressible materials all standards will have a respective weight associated with the material you are measuring.
These weights are called Dead Weights, whereby the weight is placed on the top of the measuring instrument to apply the amount of pressure required for that respective material.
These gauges can be configured with different dead weights and anvils to provide a range of contact pressures meaning they can be easily configured to meet a variety of standards.
Assigning the Correct Anvil
The size of the anvil also influences the reading. This is because anvils with bigger surface areas spread the weight across a larger surface, reducing the pressure. Luckily, anvils can be changed to meet the standards of the respective material to solve this problem.
Let us have a look at some specific gauges and the standards below…
4. Measuring Compressible Board & Paper
The DML3801C and DML3801P Bench Gauges are perfect for measuring cardboard and paper. The DML 3801C and DML3801P Bench Gauges are board & paper thickness gauges designed to meet the requirements of the following standards:
- ISO 534 Paper and Board
- ISO 438 Paper
- GB/T1983 Soft Paper
These gauges have a measurement resolution.
- Contact Area: DML3801C 12cm2 DML3801P 2cm2
- Contact Pressure: 100 +/- 10 kPa
- Repeatability: +/- 0.004 mm
5. Measuring Films, Foams, Paper and Board
The more versatile instruments for measuring films, foams, paper and board are normally Handheld Gauges.
There are many variants available, some small some large. Some gauges are specifically designed for use on sheet material and will often feature large throat depths. This is so a measurement can be taken towards the centre of the sheet.
DML3031FF is a gauge designed to measure thin films, foams, Paper and board.
With a measuring range of 25mm and a resolution of 0.01mm. Again it is designed to exert very low pressure on the sample being measure, utilising 55mm diameter anvils to achieve this.
C12100T Hand Held Gauge
C12100T This gauge has a throat depth of 554mm, a measurement resolution of 0.1mm and can measure up to a thickness of 100 mm. The force applied varies from 1.6N - 2.2N. It is ideal for sheet materials. Contact anvils are 50mm diameter, designed to reduce pressure. Some other variants in this range are shown below.
Kroeplin C110T (0-10mm) External Caliper
Kroeplin D450T (0-50mm) Foamed Materials & Foils Measurement Caliper
Kroeplin D220T (0-20mm) Foamed Materials & Foils Measurement Caliper
Overall, there are three main considerations to make when measuring compressible materials.
The first, research the standards that are relevant to your measuring application.
The second, research and find the right measuring instrument that is suitable to your requirements.
The third configure the instrument to meet the standard being used (if this hasn’t already been done). This may involve applying the correct weight or measuring anvils to the gauge.
I hope you have enjoyed this article and remember if you have any questions then please leave comments or contact us directly and we will be more than happy to assist you and provide you with professional advice to meet the needs of the application you are measuring.