GTW Developments Ltd - New company, new ideas.

New users - cutting yarns

Most pneumatic splicers have one or more cutting knives.    Knives are useful because they allow the operator to place yarns into the splicing head without taking too much care, secure in the knowledge that the splicer will trim off the excess unwanted yarn.
Though not part of the intermingling process itself, cutters perform a very important function in a splicer, and if they are not effective, they can ruin the splicing performance.

The primary function of a splicer is to make an unobtrusive joint.   In the case of the standard ends-opposed splice, the profile of the joint itself should be as flat as possible;  in addition, the "tails", fibres projecting out of the ends of the splice, should be as small as possible.   If the tail on either side of the joint projects too far, and is too "fluffy", then the tail may get caught in a needle eye, thereby defeating the whole purpose of the splice.

The chances of getting an unobtrusive tail are maximised if the cutter knives are effective.   If the fibres on each side of the joint are cut efficiently, cleanly, and quickly, then the splicing action is more likely to draw in the fibres on either side of the joint, thereby causing the tails to become small or invisible.    If the cut is poor, one or more fibres will remain un-cut, thereby making the splice rough and untidy, and the tails long,   In extreme cases, very poor cutting can completely ruin the splice.
 
And when is cutting NOT used?
Most pneumatic yarn splicers, regardless of the manufacturer, conform to certain design norms.  
They have:
  • a body, which serves as a means of gripping the tool, and a means of delivering air to the system
  • a splicing chamber, which serves as a means of accomplishing the intermingling process
  • a set of cutting knives, which serve to trim off excess yarn, and to present the yarn ends to the splicing chamber in a suitable configuration.
Despite the well-understood importance of the cutting knives in splicing, the knives can actually impose some limitations on the process.  
In most splicers, the cutting knives are mounted in fixed positions; this is understandable, because the knife drive mechanism usually has a fixed geometry.   The result is that most splicers have a knife separation of around 30 mm, so that the splice is also about 30 mm long.

As yarns increase in size, a problem of “scaling” begins to appear.   Ideally, all splices, regardless of the diameter of the yarns, should have a similar geometry; it then follows that – in rough terms – the length of a splice should increase in direct proportion to the diameter of the yarns being joined.   As yarns increase in size, strict performance parity can only be achieved by making a corresponding increase to the size of the splicer, and the separation of the cutters.   For example, this company normally splices 100 tex polyester on a 25 mm splicing chamber with a 30 mm knife spacing.

Strict scaling would suggest that a 10000 tex roving would need a splicing chamber 250 mm long and knife spacing of 300 mm deep.    This is unsuitable for a factory environment..

A subsidiary problem, but one which is probably more important than chamber design, is the provision of appropriate knives. Even if the matter of knife separation is solved, eventually we shall encounter a yarn which is either too big or too tough to be cut.   These two problems together seem to define an upper limit for yarn count which can be spliced.
However, we have evolved and patented a solution which eliminates the need for both large chambers and large knives. The notion is simply that of drawing the splice through a small splicing chamber for an arbitrary distance, thereby making a splice of arbitrary length.
 

The yarns are not cut by integral knives; they are merely cut in advance, and overlapped in the splicer; the action of drawing the yarns through the splicer then draws the filaments together.   The need for integral knives no longer exists.

Conventional wisdom has it that the yarn should sit neatly over the top of the blast hole in order to make a good splice. Our experience is that moving the yarn relative to the splicing chamber during the splicing operation, while it makes the joint less attractive, does not seem to do much damage to the splice strength.

Yarn can be drawn through the splicing chamber manually; this is the basis of our Model 110.   The 110 works perfectly well, and sells in considerable numbers for yarns of up to 6000 tex.    It is being further developed, for materials of count up to 10000 tex.