Sunday, April 25, 2010

Fiber Evaluation (Staple Length/Variation)

In our last post we began a 7 part series looking at the critical categories that should be evaluated when considering a fleece for fiber processing. Tensile strength is definitely the first, and in my opinion, one of the most important aspects of fiber evaluation, but our critical area today comes in a close second - staple length & variation. I've purposely chosen to combine both the length of the fiber and the variation in the length as one category.

Length plays an important role in fiber processing at four different points: opening, carding, drafting and spinning. At each of these points I will share how overall length and variation in the length impacts each of these four areas. As your friend in the industry I hope that through this post and the others in this series we can better understand the implications and develop sustainable standards, and ideal breeding benchmarks regarding length and variation in length and how it will impact the process of "paca to product".

In order to develop a common perspective with all my readers let's assume the following scenario. You are an alpaca farmer who raises 15 Suri alpacas and every year you have your fleeces shorn and processed into 3 ply fingering weight yarn. There is however one exception - you have one or two suri alpacas that you will take to the show ring and so you don't shear their fleece until the end of year two to have the best presentation in the show ring. Assuming this perspective will allow us to better grasp the impact that processing will have on your fleeces.

Now it's currently Spring and if you haven't already shorn your animals you will be shortly. Harvest time for many is a necessary evil or at best a much anticipated time but latent with potential problems and obstacles that need to be successfully navigated. Needless to say the harvesting of alpaca fiber plays a critical role in the value added chain and significantly impacts its processing performance.

But let's think happy thoughts for a second - let's say: your son does all your shearing & skirting for free and as a certified professional does an excellent job, your animals are all pure white, they have 18-20.9 micron fiber, which produce 6 pounds of usable fleece, and you have a host of customers who are contacting you weekly to find out when this year's clip will be processed into yarn so they can get their hands on that lustrous, silky smooth yarn that they just love, oh and your mill has just a 4 week turn around time and a great price! Like I said we're thinking happy thoughts here.

So here you sit in your dining room (which has been converted into your sorting facility) with three distinct groups of fiber in front of you ready to take down to the mill. Now all the fibers are identical in every way except that their staple lengths are drastically different. You have one group of fleeces that has 13 to 15 inch Suri fiber from your two year old show ring animals. You have another group that has 2 to 3.25 inch Suri fiber from your seven year old girls who still produce amazing offspring every year. Finally you have the third group, which makes up all the other fibers in your herd, and they have 4 inch, 5.5 inch and 7 inch fibers.

So what happens to these three groups during processing and how does their staple length and variation impact their processing performance?

First, it's important to understand that any fiber in mill processing going on to yarn will follow the same basic steps regardless of what mill it is processed at: tumbling/scouring, drying, opening, conditioning, carding, drafting, spinning, plying, skeining and fulling. Certain mills have additional steps but this is the basic process that the industry follows.

The first area in which staple length/variation will have a significant impact is at the opening stage. Opening is the stage in fiber processing where each clump of fleece is separated into individual fibers so that it can be carded most effectively and efficiently. But the question is how does length effect the opening process and what kind of impact does variation in length have on this process as well.
Let's start with the 13-15 inch show animal fleeces. I am not a judge nor do I show alpacas in the show ring, but from listening to our customers these are some thing that I have learned. As show ring alpacas one of the areas they were evaluated on was the consistency of their lock structure. In the show ring points can be taken off for fleeces that do not demonstrate the same consistent lock structure across blanket of the animal and ideally across the whole animal. The type of lock structure (flat, tightly twisted, loosely twisted, etc) is not as critical to the judges as this consistency issue. This benchmark finds itself in conflict with many stages in fiber processing and opening is one of them.

Tightly and even loosely twisted locks are virtually impossible to open by machine without damaging the fiber. Each of these individual locks have to be opened by hand before they can be run through the picker or the fiber separator. This becomes a conflict in processing due to time - and in processing time is money. Opening by hand the individual locks of suri increases the time greatly. On standard length (4-7 inches) fibers it can double the amount of time it takes to open them. And on extra long length fibers (especially 13-15 inch) can multiply the job exponentially! I once opened a 24 pound lot of 10+ suri locks which took me 2 weeks to open because they were so tightly twisted together. Typically in our mill we open between 20-30 pounds of fiber per day. For this very reason many mills reject long suri fiber that has a tightly twisted lock structure, while others place additional charges to the processing cost. While standard length suri fibers with a twisted lock structure are harder to open they are not impossible. Ideally, from a processing perspective, suri will have a flat lock structure (or minimal twist) allowing their processing time to be no different than huacaya. Another great way to test how quickly it will process if try opening a single lock by hand. How easy was it to pull it apart?

All that to say that length (when coupled with a twisted lock structure) can have a significant impact on the time incurred in the opening process.

Well enough about lock structure we were talking about length and variation in the opening process. The opening process is such that your fiber will be thoroughly reshuffled when it is done being open. It will be impossible to tell from what part of the animal a certain fiber came from. So when fiber is sent in and there's greater variance than 1.5" in the staple length, as is the case for fibers that are 4", 5.5" and 7". If these fiber lengths were all in the same bag for processing you can bet that they will be even distributed after the opening stage is completed. This doesn't pose any kind of problem at this stage in the processing but compromise the quality of the finished product on down the line.

In the last group of fibers that are 2" to 3.25" we experience no problems in opening or individualizing the fibers and because they are within a 1.5 inch variance they will not do anything to compromise the quality of the finished product later in the processing of the fiber.

The next major step in processing where length is an issue is in the carding stage. Carding is the process where individualized fibers are kept separate while gently combing them through a series of rollers called workers and strippers as they travel clockwise around the main drum called a swift. (see diagram) Fibers that were previously opened and individualized are now combed and brought into a more parallel direction (see diagram below). In the mini mill system this degree of alignment is within 30 degrees of completely parallel.

Short fibers under 3.5 inches quickly align themselves with each other, while longer fibers take more time. Consider how long it takes to align long hair with a comb as compared to short hair. After one pass at the carder long fibers may not have been effectively aligned, while shorter fibers (under 5 inches) have carded at peak efficiency.

Another potential problem with long fibers at the carding stage is fibers that are longer than the two points of tension or "pinch points". In the case of the Belfast mini-mill system the pinch points are where the fiber leaves the swift at the worker and where the stripper transfers the fiber back onto the swift. (see diagram above) From my observations a fiber which has a length longer than 12 inches will have a high tendency to do one of two things: wrap around the stripper with the end of the fiber trapping the beginning of the fiber and not allowing it to be transferred onto the swift, or the fiber will be broken when the stripper is trying to pull it off the worker but the end of the fiber has not yet left the pinch point between the swift and the worker.

In our next post we will look at how staple length and variation have an impact on the drafting and spinning processes. I hope this has been helpful for you to better understand why fiber must be evaluated in this simple 7 step process of Strength, Length, Micron, Crimp, Vegetable Matter, Dust, and Second Cuts. By evaluating these 7 areas in your fleeces prior to processing (and even prior to shearing) you can minimize your farm costs and maximize your profits from the value added steps a mini-mill can provide.

Your friend in the industry,

1 comment:

Patrick Carter said...

Thanks for sharing!

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