The degree to which you interlock the fibers depends on the needle type and efficiency of the needle style used. As the needle begins to wear, it becomes less efficient and will affect the quality of the product being produced.

It is difficult to estimate the life of a needle in a typical production line. There are many factors which will influence the actual needle life. Some of these factors are:

The ability to reproduce a uniform quality product on a continuous production basis depends greatly on the consistent efficiency of the needles used in order to effectively interlock fibers.

As the needle is being utilized, over a period of time the barb angle will start to wear away to the point where there is insufficient fiber transportation to effectively interlock fibers and produce the desired physical properties in the web.

The following graphs will show how a needle will wear and the effects this decrease in efficiency will have on the quality of the product being produced.

There are several different methods of needle replacement/rotation. The most common methods are:

1. Complete replacement of all needles on the needle board when such time the needles are worn to the point they will no longer effectively interlock fibers.
   
   
2. After determining the needle life when producing your particular product, a section of needles is replaced after a predetermined amount of hours or strokes. Graph "B" is an example of this method of needle replacement based on an estimated needle life of 30 million strokes.
   
   The needle board is divided into 3 sections (A, B & C). After 10 million strokes you would replace all needles in section "A" and broken needles only in sections "B" and "C".
   
   After another 10 million strokes (20 million total) you would replace all needles in section "B" and broken needles only in section "A" and "C".
   
   After another 10 million strokes (30 million total) you would replace all needles in section "C" and broken needles only in section "A" and "B".
   
   After another 10 million strokes repeat replacement with section "A".
   
   
3. After a predetermined amount of time or when there is a noticeable difference in the quality of the product being produced, only the broken needles are replaced.

The effect each method of needle replacement will have on the quality of the product being produced is shown in Graph "C". As shown, this method of replacing needles by section is far superior for producing a consistent, quality product.

The graph for method number 3 is not shown due to the very unpredictable results of this method. Although on most products the results would probably follow closely to method number 1, it would depend solely on the amount of broken needles replaced and the timetable chosen for this replacement.

Which method of needle replacement will be most effective in your operation? To determine this, a complete product quality and economic study should be made.

If there are relatively wide tolerances concerning the quality of the products being produced, then perhaps the economics of a sectional needle replacement program are not justified.

On the other hand, if the products produced are expected to meet or perform to a narrow range of tolerances for specification such as permeability, thickness/density or aesthetics, and the reproducibility of these specifications is an inherent part of products being manufactured, then needle wear needs to be determined and an effective needle rotation program put in place.

Foster Needle Company offers technical service in determining needle wear, and assistance in determining the proper needle rotation program that maximizes needle efficiency and ensures the reproduction of a quality product.

Foster Needle will evaluate needles at specified intervals and determine needle wear and remaining needle life. Based on the results of this evaluation, Foster Needle will recommend the proper needle rotation program.

As mentioned previously, there are many factors in the production process that will affect needle wear. The total amount of strokes obtainable before the efficiency of the needle becomes inadequate can be as low as 1 million strokes or as high as 100 million strokes depending on these factors.

Foster Needle will recommend the correct needle style for your products as well as the technical service and assistance in producing a quality product.