3rd Apr 2023
FAQs: Cardboard Cores and Tubes
Our customers often ask questions about cardboard cores and tubes. Everything from: How environmentally friendly is cardboard? to What’s the difference between a spiral cardboard tube and a convolute cardboard tube?
So, we’ve created this cardboard tubes and cores FAQs blogpost just for you. And you’ll also find more questions and answers on our FAQs page here.
Manufacturing and durability
How are cardboard tubes manufactured?
Spiral tubes and convolute tubes have very different production methods and machinery. At Stell we make both types.
Spiral cardboard tubes are made by coating the top side of ribbons of cardboard (also called webs or plies) with an adhesive, then winding these in a continuous process around a steel mandrel using a rubberised winding belt to pull the board around the mandrel. A flying knife is then used to cut the tubes to a desired length whilst the tube is being continuously wound.
Convolute cardboard tubes are made using a single sheet of cardboard. Typically, this sheet is unwound from a jumbo reel and guillotined to the required length on the machine. The width of the sheet is dictated by the width of the jumbo reel. One side of this single sheet is then coated in adhesive before the ‘lip’ of the paper is fed into a grooved mandrel. The mandrel is then rotated, and the board wraps around the mandrel, forming the tube. The tube is then doffed off the mandrel and the machine is ready to start the next cycle.
At Stell, we have the UK’s largest Cardboard tube tooling library with over 200 spiral spindles/mandrels and over 250 convolute spindles/mandrels.
What’s the difference between a spiral tube and convolute tube?
Spiral and convolute cardboard tubes have very different manufacturing processes. They are also quite different visually; a spiral tube normally has an easily identifiable spiral mark on its outside where the outer ribbon is spiralling next to itself (‘butt-jointed’) or where there is an overlapping ‘cover’ (thin ply) of paper on the outside. In general, spiral tubes can be manufactured to tighter tolerances with a higher quality of finish than convolute tubes.
A convolute cardboard tube is made from a single sheet of paper with a straight seam running down the length of the tube. This seam is not always easy to spot if it has been ground to a feathered edge. Due to being made from a single sheet, convolute tubes are more restricted in their geometric range than spiral tubes.
However, the single sheet fabrication of convolute tubes gives them two distinct advantages: firstly they can withstand higher internal pressures (important for pyrotechnic uses) and secondly they have a higher beam strength (compared with the equivalent spiral tube) which means they can be a cheaper option for many textile and material processing applications where beam strength is an important part of the specification.
What are the dimensions used to define a cardboard tube?
At Stell the dimensions we use are as follows:
The length is measured with a tape measure to the nearest mm for tubes of length 300mm and above. For tubes less than 300mm, a vernier is used to give a length to the nearest 0.1mm.
Inside Diameter (ID)
The inside diameter of a tube is governed by the size of steel spindle that the tube is wound around. It’s very difficult to check an unknown ID accurately with a vernier, so we also use plug gauges that slide inside the tube or core.
Verniers can be used as a guide but, if the ID is a critical dimension, we always ask our customers to send us a sample of their tube, where possible, so we can use our full range of plug gauges to accurately match their requirement to the exact ‘spindle’ size required.
This is the thickness of the wall perpendicular to the circumference of the tube. It’s relatively easy to measure with a vernier, although care must be taken to ensure consistent readings.
Outside Diameter (OD)
The outside diameter of a tube is used instead of wall thickness for any tubes that must fit inside a component. We can manufacture to tighter tolerances on the OD than the wall and the OD is easily measured with a set of verniers.
How is the Inside Diameter (ID) of a tube measured?
It’s difficult to measure the ID of a tube accurately using vernier callipers. Verniers can be used as a guide but, if the ID is a critical dimension, we always ask our customers to send us a sample of their tube where possible so we can use our full range of plug gauges to accurately match their requirement to the exact ‘spindle’ size required.
What’s the difference between a cardboard tube and a paper tube?
Nothing! Some people use the term cardboard tube and others use the term paper tube – both are commonly used. Generally, cardboard is thought to be a ‘thick’ paper but there is not universal definition of what ‘thick’ means. Most of our tubes are made from a material that most people would call cardboard, so we call them cardboard tubes. That said, looking at some of our marketing material from the 1920s, we were described as paper tube manufacturers!
Are different qualities of cardboard are used to manufacture tubes?
Yes. Broadly, there are four aspects of board quality that must be considered for cardboard tube winding: there are the strength, thickness, and surface characteristics of the board but also the consistency with which a particular mill maintains these characteristics. We use a large range of cardboards with different strengths, thicknesses and surface characteristics. But we only use suppliers that can deliver these consistently. One of the benefits of being 150 years’ old is the organisational knowledge and experience of suppliers, mills and materials that this brings!
For example, this experience allows us to tailor products precisely to our customers’ requirements: if you need extra strength but are constrained by the Outside Diameter (OD) size, we can specify a stronger board. Or perhaps you need a tube with a particularly tough inside ply to prevent damage on a driving shaft? We can suggest different options for this too.
How strong are industrial-grade cardboard cores?
This is a bit like asking: how long is a piece of string? We tailor the strength of our tubes to the particular customer or market into which we’re supplying. In essence, the stronger you make a tube the higher the material cost. On one hand we’re careful not to over-specify our tubes, and on the other, the risk of mechanical failure of a tube must be minimised due to the high value of the materials being wound onto or protected by the tube. The trick to getting this balance right is to minimise the variance in strength of the tube so that once you’ve finalised the specification you know it will be right, consistently. Variance in strength can be caused by varying paper quality, varying adhesive quality and varying quality of manufacture. And this is what we work hard to minimise with a passion at Stell – great people, great materials, great equipment = great consistency.
And we can quantify this using crush testing and beam strength testing.
Are cardboard cores and tubes water-resistant?
No, because cardboard, by its very nature, absorbs water. But there is a wax dipping process that can provide a level of water resistance. This can be useful for pyrotechnic applications or where the tube life needs to be extended.
Environmental considerations and sustainability
Are cardboard tubes and cores recyclable?
Yes absolutely. Cardboard tubes and cores are considered one of the most environmentally friendly types of packaging because they are made from a renewable source. Cardboard is one of the materials with the least environmental impact. It is 100% recyclable and 100% biodegradable.
What happens to cardboard cores when they are recycled?
The cardboard is collected by either a waste merchant, or the original manufacturer before being sent back to a board mill where it is graded for quality, sifted for contaminants and then re-pulped (shredded and mixed with water). Then it is fed back into the paper making process.
What is the most eco-friendly packaging?
Any paper-based packaging is rightly regarded as being amongst the most environmentally friendly and sustainable.
How are cardboard cores used in different industries?
Cardboard cores are used in many different industries and processes. Almost every single type of tube or core has probably been used in some sort of industrial application from textiles and carpets to tapes, labels, and films.
And each one is different. For example, cores for wrapping paper and packaging don’t need to be as durable or strong as heavy duty cores you’ll find used in the flooring industry.
Convolute or spiral tubes used for pyrotechnics must be manufactured so they are safe and reliable. And for flexible films we know it’s important to manufacture them with the appropriate levels of crush strength.
If you want to know more about how we add value to manufacturing and supplying cardboard tubes in your industry please get in a touch!
What’s the difference between a cardboard tube and a cardboard core?
Some people say tubes some people say cores – the words core and tube are largely interchangeable. But in the industry, we generally class cores as a tube that has been cut to a shorter length, and tubes are longer. But where ‘shorter’ becomes ‘longer’ is down to personal opinion!
Why choose Stell for your cardboard cores and tubes?
There are many reasons why customers choose Stell for their cores and tubes. Above all, we add value through our service, consistency and technical knowledge to tailor our whole approach to your individual requirement whether that be through supply chain / delivery flexibility, technical knowledge, packaging or the finishing characteristics of the tube (cutting, printing, embossing, slotting). Take a look at our blogpost on why choose Stell here.