AS contract manufacturers of a wide range of bespoke powder, granule and liquid chemical products, we work with numerous raw materials and substances.
All are different so understanding how they are composed and could potentially react during the manufacturing, packing or even transit process is critical if we are to achieve our customers’ desired end result.
Understanding the density of substances we use during manufacturing is key, but just what do we mean by density and how does it impact what we do? Read on to find out…
What is density?
Density is a measure of how compactly a substance or object is made up. It tells you the mass of a substance from a known volume and applies to both liquids and solids appearing as grams per millilitre (g/ml) or kilograms per cubic metre (kg/m³).
When you know the density, you can calculate the mass of a substance from its volume and, likewise, can determine the volume when its mass is known. (See below for calculating with density).
Understanding the density of a substance is important when it comes to manufacturing as it can impact the quality of the product being made.
For instance, with solid materials like powders or granules, differences form in terms of particle size and shape when they are mixed or agitated. These particles settle differently each time they are moved with varying air gaps between them. Solids can be compressed, pushing out the air to make a greater mass in a smaller volume; this increases their density.
Density in solids is termed either ‘tapped’ or ‘bulk’. Those solids which have either been compressed or settled with no air between the particles, have tapped density. Others, where the volume of a substance has settled as it has fallen, has bulk density.
Calculating with density
Our understanding of density can be boosted with some calculations:
To calculate mass:
- Take a container and fill it with liquid to the one litre mark.
- Multiply the volume by the known density 1.2kg/L.
- You then have the mass of the liquid: 1L x 1.2kg/L = 1.2kg
To calculate volume:
The opposite is true when calculating volume from mass:
- Weigh out 1kg of the liquid – this is your mass.
- Divide by the density 1.2kg/L
- You then have the volume of the liquid: 1kg ÷ 1.2kg/L = 0.83L
To calculate density:
Where you know the mass and volume of a substance, you can calculate its density by dividing the mass by the volume.
For instance, 1.0kg (mass) ÷ 0.5L (volume) = 2.0kg/L (density)
Measuring density
Measuring the density of a substance can be a useful indicator of how it is composed. For instance, it could tell you how much of a soluble material like salt has been dissolved in a solution or, with a dry product, how much liquid it might contain.
Hydrometers or pyknometers are largely used to measure liquid density while, with solids, weighing a known mass into a measuring cylinder and taking note of the measurement will give you its volume, from which its density can then be calculated.
To find out the bulk density, take your measurement as soon as the solid has been poured into the cylinder. For tapped density, tap the cylinder several times to encourage the air to escape and the product to settle before measuring.
Knowing the density can be fundamental to deciding what size bag or container needs to be used to package it. For instance, a kilo of sand will be far denser than a kilo of feathers and will require a smaller (but stronger) bag than that needed for the feathers.
Did you know?
Here are some useful tips and facts regarding density:
- Water is a unique substance with a density of exactly one (1.00g/ml) at 20°C ie 1kg of water is exactly 1L.
- Oils and solvents float on water because their density is generally lower than water.
- Liquid density can be highly sensitive to temperature – as shown by the old school mercury filled thermometers! They should only be measured when at the required temperature.
- Specific Gravity – or SG – is a term sometimes used to describe density. It refers to the ratio of the density of water to the density of a sample at a set temperature.
- Emulsions and suspensions can be particularly variable in terms of density especially where they have become aerated. It is important to allow for any changes that may have occurred post-manufacture such as during storage.
- Density can change in those liquids which can experience a ‘drop out’ reaction or maybe react by giving off a gas.
- Beware of moving high density liquids! They will weigh far heavier than those with a lower density.
- Solids have varying density values depending on whether they are powdered, granulated or form a solid mass. For instance, a bar of gold has a density of 19.3g/ml compared to the same volume of powdered gold which has a far smaller density of 0.85g/ml.
- With those solids made up of different sized particles, fine particles will sink leaving coarser ones to lie on top. The density will therefore vary depending on from where in the container the sample is taken for testing.
At Grotech Production Ltd we have some 40 years’ experience of working with raw materials of varying density, blending and packing them to form the optimum product for our customers. If we can do the same for you, why not give us a call on 01405 761746 or send us an email here.
