Rod and Blank Production
by Dr. Steve Harrison
Here at Harrisons we start the production process with a roll of flat carbon fibre prepreg, that is carbon pre-impreganted with epoxy resin, and turn it into fishing rod blanks. It is a process I still find miraculous, the conversion of a flexible, almost "floppy" raw material into a stiff light precision instrument. There is nothing more rewarding than making things of quality, and here we describe how we do it. (Though we will not be giving all the secrets away!)
We buy-in carbon fibre prepreg from companies who manufacture it to our specification. The fibre type, weight of fibre and resin content are all controlled by us. Many of you will be familiar with wet lay up of glass fibre when the resin is added to the dry fibre at the point of manufacture. Our process is quite different. Using pre-impregnated carbon has many benefits over wet lay up. One of the most important is that resin content is precisely measured in a controlled environment. This is far more accurate than adding resin in the workshop. It means that the resin content can be kept lower, saving weight. The other big benefit is ease of handling. Dry carbon is awkward to handle and control. Wet resin is pretty unpleasant. Prepreg is by comparison pleasant and easy to handle and can be carefully cut and precisely laid into place.
Carbon prepreg is expensive stuff. A 50m roll can cost thousands of pound, and we consume kilometres of it each month. The resin, a modified epoxy system, does not cure at room temperature, but needs heat to make it solidify. This means the prepreg will not cure at room temperature and can be refrigerated to keep for very long periods.
Carbon fibre alone, is a black floss like material, very vulnerable to abrasion and damage. It is only by combining it with a resin system that we get a composite that is useful as an engineering material. So when we talk loosely about carbon fibre fishing rods we normally mean carbon fibre and epoxy composite, but that is a bit of a mouthful!
Chemically and physically, carbon is an interesting substance that has the ability to bond one atom to another in several different stable ways by virtue of it's covalent bonding properties. Diamond is made of carbon and is one of the hardest substances known to man. Carbon fibre has the carbon in long chains to produce excellent tensile properties. By the way, the Americans and much of Asia calls carbon fibre graphite. Graphite is actually a totally different form of carbon with flat sheet like molecules which have lubricating properties. More recently carbon has been formed into new stable forms such as nano-tubes and buckyballs.
Few prepreg suppliers specialise in supplying small companies with off the shelf products, most run larger quantities of prepreg to the exact specification required by their bigger customers. This makes it a very hard industry for anyone to enter. Harrsion's are one of the bigger non aerospace users of prepreg in the UK. We have buying power that allows us to make great demands on the input quality of raw materials. We believe that material we currently buy is the best available. We source different prepregs from different places, and are pioneering the use of metre wide prepreg in the UK. This means less waste for us and better value for you.
Prepregs differ in fibre type, orientation and properties, resin content, and weight per square metre. At any one time we have about ten materials in use. Most have fibre in only one direction, though some combine two fibres at different orientations. We do not make a rod with one fibre from tip to butt, but use different prepregs throughout the rod, often combining three or four in one rod. The reason for this is because different parts of a rod do different things. The tip for example requires fibres to stretch more as it bends into a curve.
Below is a list of just a few fibres and their properties when put in to a test laminate. Units vary from country to country, the UK favours measuring strength and modulus in Pascals, whilst USA uses perhap the more intuitve pounds per sq inch. It has also become common to refer to fibres as 24ton, 30 ton, 40 ton etc. In the table below M30 is a 30 tone intermidate modulus fibre and M46J a high modulus fibre with less stretch but also less strength.
Table from Toray http://www.toray.com/
Carbon Fibres come in a variety of types, and brands. IM6 and IM8 were heavily promoted at one time, but other major products are, M55, M40, M40J, M46J, T300, HR40, a long list. Each producer, and there are many, has its own brand of fibre that may be equivalent to a fibre from another maker. These fibre types vary in properties when they are tested on their own, putting them into a composite structure complicates everything and the strength and stiffness becom more dependent on the fibre orientation and resin properties.
So what is fibre modulus and strength. Modulus, is in effect "stretchiness". It is different to strength but can easily be confused. When you make a composite using high modulus fibres, you make a stiff tube or rod. When you make a high strength tube, it may bend more, but it will bend further before failing. Think of an elastic band that stretches when you hang a weight from it. The amount of stretch is proportional to the weight. If you look at how much stretch you get for the added weight and use the cross sectional area of the rubber to convert this into a constant for all sized rubber bands, you have a measure of modulus. Carbon fibres stretch very little, that is why they are so useful, but the amount of stretch can measured and varies from a low modulus fibre to a high modulus fibre.
Strength is much more easy to understand. It is how much weight our rubber band or carbon fibre can support before it breaks. As a rule of thumb, with carbon fibres, as modulus increases, strength declines. That is why there is no one best fibre. That is why you cannot say a 50 ton rod is better than a 30 ton rod. And by the way, when a fly rod is branded as 50 ton, it will typically only contain a relatively small amount of this fibre, just as boron fishing rods only used to contain small quantities of boron.
Fishing rods across a range of applications need high strength, high modulus and intermediate fibres to perform well. No one fibre is superior. High modulus though often more expensive, is less preferable than a cheaper fibre in some applications. If you had to name one great all rounder fibre, it would be the T800/M30 family of intermediate fibres which are both extremely strong and have an increase in moudulus over standard high strength fibres.
So I assume that rather than clearing things up I have raised more questions than I have answered. This is why here at Harrisons we tend to be a bit vague about where we use different fibres and what they are. This is for two reasons. One, we believe we are ahead of the game, and we do not want to help our competitors. Two, it is almost meaningless to the angler because the picture is so often confused by the claims of the companies that outsource rod blanks and rods.
In summary therefore, I can say that there is no one best fibre. It makes no sense to use one fibre throughout a rod. When companies claim they use a certain fibre such as 50ton, they generally mean the rod contains some of that but not neccesarily througout. And finally, I recommend that you ignore the marketing blurb, pick up a rod and judge it on what you think and what you have heard. Is it well balanced, does it cast well, is it well made etc.
Making a Blank
Design is the first step. That is the most secret bit here, but one important ingredient is experience. There are a small handful of really knowledgeable quality blank makers in the world. We are one of them, and it was hard work getting there! So sorry, not too much information is public domain here. I can tell you we sometimes start a design with a blank sheet of paper, but more often we take an existing blank, and play around with it. Unlike those companies sourcing their rods from the far east, we have total control. We can go through a cycle of design to prototype in two hours. The importers tell you it took two years to develop a new rod. Most of that was probably spent waiting for samples. We can develop a rod here in hours. But then we test it for months.
A design has to be translated into a pattern. Like a dress design. Three dimensional tube, starts out as two dimensional pattern. The patterns are cut by hand from the prepreg. A rod section may be made from one simple wedge shaped pattern, or more often a complex lay up of irregular shapes and different materials. The subtleties of design make the difference. The little changes in taper, stiffening, the balance of materials. Particularly critical is the joint area where a Harrison blank will have a smoother transition than many cheaper rods.
The other variable besides materials, is the mandrel, the tapered rod around which the tube is formed. We have a large stock of mandrels of various tapers and size. These are made to our specification in America. We have a large number of each type, as it is uneconomic to make rods one at a time, we have to work in batches.
The mandrels are cleaned and prepared with a release agent, then the carbon prepreg pattern is rolled around it using a pneumatic rolling table. Its like rolling a giant tapered cigarette. It is not too clear in the image but blank maker Andy Mantova is preparing the prepreg on the right of the mandrel so it can be rolled by the movemnet of the tow pressurised and heated "plattens". The top platten descends and bottom platten produces the rolling motion.
After rolling the prepreg is wound under controlled tension with a high performance heat shrinkable tape. This binds the prepreg tight to the mandrel and controls the pressure during cure. The pressure is required to control resin flow, exclude air and make a high perform composite.
|The wrapped part is then placed in curing oven for a
period, during which the resin is activated, gels, and cures. Cure time is dependent on
part size temperature and resin system, a controlled cycle is measured in hours rather
Faster low temperature cure systems are emerging for boat building, but are yet to be proven in rods. Longer slower cure times are favoured by us to get maximum consolidation and stress free composites.
On finishing the cure cycle, the mandrel is extracted pneumatically, the part unwrapped and forwarded to the finishing department. Blanks may be linished using our taper sensing centreless machine, or they may go straight to trimming and jointing.
The linishing is a process used to give a smooth finish and key for painting. About half our blanks are coated with colour finishes, and about half go out with the natural unground finish.
Linishing is a simple but critical process. We have the best machinery and expert Mike Helliwell supervises this process. The aim is to remove the resin ridges but not affect the action of the blank by removing carbon.
Rod sections are fitted together after precision centreless grinding the male end of one section to fit into the female of the section above. Blanks are then ready for building.
This is a simple account of what we do. The excellence is in the raw materials, the design and finally the subtleties in production. Our staff turnover is virtually nil, our team ambitious and dedicated. It all adds up to a better fishing rod. And all the blanks are made here in Liverpool in sight of my office window.
Dr. Steve Harrison © 2009