Friday, 16 October 2015

What is ...a "Mill making"?

What is ...Number 22

Regular followers of this blog will know that in the middle of the month, I publish a "What is ....? post. The article covers various aspects of paper, printing and finishing in greater depth. However, many of these subjects are complex, so these posts are only intended to be a brief introduction to the topic.

What is ...a "Mill making"?
Many of you may have heard the term "mill making" - often it is used by printers when talking about ordering paper and the context that a mill making is referred to is generally because a a certain quantity is needed or special size or weight is required which can also save money.
However I should explain that all paper is in fact made at a paper mill and therefore all paper is the result of a "mill making"! The two areas I shall cover is mill makings of standard products and mill makings of bespoke products.
Firstly I'll just give a brief introduction to paper making. 
Twin wire paper machine
The manufacturing of paper is a mechanical process and is ”heavy industry”. The site of a paper mill covers many hectares and the machines themselves are housed in buildings the size of aircraft hangers. With the exception of mills making specialist material (such as artists papers) paper mills manufacture tonnes of papers per day. Typically a small mill might make 50 to 100 tonnes per day with larger mills making over 1000 tonnes per day. A paper machine is very large, typically 4 metres wide and over 100 metres long.
Bales of pulp on conveyor
Pulp being mixed in hyropulper
Bales of refined pulp are tipped into a ‘Hydropulper’ which breaks the pulp up by adding huge amounts of water and movement. After several more refining stages the ‘stock’, now 99% water and 1% fibre, is pumped to the start of the paper machine called the Headbox. The stock is sprayed onto a fast moving mesh which due to gravity allows most of the water to fall through the mesh. The remaining fibres are ‘matted’ together on the mesh forming a knitted ‘web’ of interlocked fibres (if you tear a sheet of paper you can generally see the fibres). The web of paper which is still about 60% moisture passes through the press section which compacts the fibres and removes more moisture before entering the drying section which finally reduces moisture by use of steam heated drying cylinders.
The web is then wound into large rolls at the end of the machine which can weigh anywhere between 10 and 50 tonnes. The large rolls are then slit into smaller rolls which can either be used for printing on the roll or cut into sheets.

It is useful to have an appreciation of the manufacturing process as explained above as it can be hard to identify with this industrial procedure in the ‘digital’ world in which we live today.

Mill makings of standard products.
Mill at Mogi Guaçu in Brazil
Many paper mills, especially the larger ones, manufacture a very limited range of products. In the most extreme case, just one product. The mill I visited many years ago at Mogi Guaçu in Brazil basically just made one product with minor variations - and that mill made 1000 tonnes a day! and produced 365 days a year - that's right, 365,000 tonnes per annum! Today that would not be regarded as a big mill.

In the case of these mills which manufacture few products, a mill will usually customise making to a special size (and sometimes a special weight) and that basically is about it! So why is this useful? Well, here are a couple of examples:

Example 1: The project you are designing for requires 50,000 sheets of 150gsm, SRA1 (640x900mm), but the paper you have selected only comes in 720x1020mm (B1). The stock (in B1) weighs 5510kgs. If you were able to get a mill making in SRA1 it would weigh 4320kgs, thereby saving over 1 tonne of paper! All paper products are sold by weight so this would represent a considerable saving.

Example 2: The project you are designing has a tight budget. You want to use a 170gsm paper but it is too much for the budget. The next standard weight down is 150gsm which you consider too light. The project requires 250,000 sheets of SRA1 paper. That quantity of 170gsm weighs 24.4 tonnes. If you had 160gsm (non standard weight) made for you as a "mill making" it weighs 23 tonnes saving 1.4 tonnes of paper. Good for the budget and the environment.

Measuring Thickness in Microns
One thing that does need to be highlighted is that paper manufacturing is a continuous, industrial process. A paper machine is not something that can be simply turned on and off and does not work to precise (or digital) type accuracy. As a result all products are made within "manufacturing tolerances". These tolerances cover everything! from variations in shade, surface, moisture, weight, size, thickness and quantity etc. 

A scale that measures the weight of paper.

For example the weight tolerance for papers is plus or minus 5%, therefore if you ordered a paper that was 150gsm, it could be made as high as 157gsm or as low as 142gsm. BUT REMEMBER THE TARGET IS 150gsm! It must be understood and appreciated that all manufactured products, be it steel, glass, plastic etc. are all manufactured to such tolerances.

Special note: Problems often occur when a product is made and is at one end of a tolerance and then a subsequent making is at the opposite spectrum i.e. The EXTREMES of the tolerance. Following the example given above, if you received your 150gsm paper and it was actually 157gsm, you would accept and judge the feel of the paper on what you had received. If some time later, you received another making of 150gsm which measured 142gsm you would quite rightly complain as the difference would be marked. However now this has been explained, I hope you can see the logic - although it is hard to appreciate at the time when there is a situation where you have never come across the issue of manufacturing tolerances before.

Quantity tolerance. As I mentioned above, a paper machine is not something that can be simply turned on and off and does not work to precise quantity. As a result all orders are made to a quantity "manufacturing tolerance". This means that when you order a quantity of paper, there is an allowance for it to be so many % over or under the ordered quantity, so this needs to be taken into account when ordering. Example: If you order 5 tonnes of 720x1020mm 135gsm that is a dead quantity of 50,000 sheets but if the tolerance is +/- 5% (for example) you would get up to 53,000 or as few as 47,500 sheets. This means you need to allow enough money to pay for the 53,000 sheets and make contingency in case the making comes up 2500 sheets short!

Mill makings of Bespoke products.
Firstly it is important to realise that to have a paper made to your own specification is a question of commitment.

As mentioned earlier, a paper mill is a large manufacturing plant. The minimum quantity required to order a bespoke paper will depend on the size of paper mill/machine and type/quality of paper to be made. It is unlikely that a paper mill will make less than 1000kilos (1 tonne) of paper and many mills will have minimum quantities of 5 tonnes, 10 tonnes or more.

There is relatively little in papermaking that has not been made before! Therefore creating your own paper around an existing specification by "tweaking" it will ensure that you get the paper that you want. It also gives the client the opportunity of looking at previously made papers which are close to the specification to be ordered thereby giving a certain degree of confidence that what the client is ordering can be produced correctly! One of the biggest stumbling blocks to ordering a bespoke paper is that it isn’t possible to see an exact sample before ordering. Generally a client can be shown samples on which placing an order depends. If there is a bespoke shade, a laboratory sample (about 5cm square) made using pulp and dies is produced, if there is a texture, a previous sample can be shown and smoothness/roughness can also be demonstrated by previous examples.

Building a specification: There are many things that can be specified, although if you just want a paper in a certain shade and weight, it might be a fairly basic specification.

Common things to be specified are the shade, substance (gsm), caliper (thickness), texture, smoothness, porosity, opacity, strength (burst) plus other criteria such as recycled/FSC content and whether inclusions and fibres are to be added etc. Other considerations are the end use, how it is being printed, sheet size etc..

Sample representation: The laboratory sample plus texture, weight samples etc. are representations of the way your paper will look and is the closest thing that the mill can supply as a ‘proof’, without making the actual paper. If you watch the video about CRUSH (above) it shows a paper sample being made in the lab.

An order can only be processed on the basis that the customer is happy with this representation but it must also be noted that paper is mechanical process made using natural fibres and water, therefore it a curious mix of skill, art and science and can never be exact.

Sample Approval:  If you approve the sample/representation, you will be required to agree to the samples supplied and the order will be placed on that basis.

...and now for the advert!
Fenner Paper has over 30 years experience in dealing with bespoke manufactured papers for Annual Reports, specialist packaging (luxury boxes), and other items such as security papers, watermark papers and even ammunition paper! We work with you to build the specification for the required material and select the right manufacturer to work with ...if you want to give it a try, just get in touch!
Posted by Justin Hobson 16.10.2015

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