One of the most important steps in staple fiber production is crimping, and that starts with the crimper pulling the tow band into the crimper. Unfortunately, there are times that process engineers and maintenance personnel find this process challenging because there are input failures. These failures are referred to as dropping the tow or losing ends. The tow jams, or packs, in the crimper, causing the operation to be interrupted. Then, valuable time must be spent mitigating the problem and getting the line running again.
Fortunately, most issues that occur with tow crimpers are not due to issues with the machinery. Rather, they are usually a result of pre-crimper tow conditions. In fact, there are many fiber manufacturers who operate tow crimpers for months straight without ever having the experience of tow input failure.
What Causes Tow Input Failure?
Essentially, there are two main causes of tow input failure, improper tow presentation and improper pre-crimper tow tension.
Improper Tow Presentation
For crimpers to work properly, they have to maintain very small, consistent clearances between the rolls. If the tow that is presented has a difference in thickness of even one millimeter, the crimper cannot grip the tow in a uniform manner and move it into the stuffing box. Instead, with uneven tow, the thicker parts will be gripped, while the thinner parts will slip. The tow will turn in the stuffing box, and the crimper is then jammed.
Here are some questions to help you narrow down the cause of the issues in your process, both at the start and end of the drawline.
Placement of subtows on the first roll of the drawline is critical to tow presentation at the crimper:
- Are you slightly pre-tensioning each subtow so that it guides properly and stays in place throughout the process?
- Are the subtows precisely placed on the first roll with individual guides?
- Are the guides distributing the tow on the roll uniformly, subsequently controlling the width of the tow at the crimper?
- Do the operating procedures define exactly the subtow placement?
Tow at the end of the drawline as it approaches the crimper:
- Have you removed perpendicular guide bars that push the tow so that it bunches on the edges?
- If your process involves stacking multiple tows, is the procedure defined to create a uniform pre-crimper tow?
- Are you depending on the crimper entrance guide to squeeze down the tow, rolling the edges? Or is the tow entering at about the same width as the crimper rolls?
- Is the tow coming out of the stuffing box moving uniformly across the width of the exit? Does either side move faster than the other because there is more tow on one side or in the middle?
- Is the crimp level across the stuffing box uniform?
Improper Pre-Crimper Tow Tension
Unlike tow presentation, which is easily monitored visually, you can’t recognize tow tension issues just by looking. Once the tow band is tight, you cannot determine the actual tension visually. The pre-crimper tow tension should only be as high as needed to guide the tow through the tow stacker and into the crimper. If the tow is being delivered from a drawline, then the tension should only be high enough that it maintains contact with the last roll of the drawline.
Because there are specific pre-crimper tow tensions that must be maintained and that tension cannot be determined visually, every crimper installation should include a dancer or tension roll to measure the actual tension. That allows the tension value to be integrated with the crimper speed, and proper tension is maintained. The proper control of pre-crimper tension frees the crimper to crimp fiber properly.
The following questions will help you narrow down pre-crimper tension issues in your process:
- Is the dancer running in the proper control range? Is it pulled to the end of travel?
- Is the tension roll or dancer actually controlling the pre-crimper tension, or has the system been bypassed?
- Is there a documented operating procedure for setting the pre-crimper tension? Is it being followed correctly?
- Does the surface speed of the rolls equal the speed of the drawline’s last roll?
- What is the tension setting? Is it correct?
Ensure the Proper Operation of Tow Crimpers with DM&E’s Expertise
Fortunately, incidents of tow input failure are nearly always a simple reaction to the condition of pre-crimper tow, and not mechanical problems with the crimper itself. This is good news for fiber plants around the world. With the above information, most issues can be resolved without lots of downtime and pricey repairs.
At DM&E, our expert staff can help you determine if the tow input failure you’re experiencing is truly a repair or replacement situation or if there is another explanation that is an easier fix. Contact us today for help.