Cleaning has one goal: to return a dirty spinnerette or pack part to its original condition in the most economical and practical manner possible.

The cleaning of extrusion equipment is becoming increasingly more critical to the Fiber Industry. Naturally, in most fiber plants the majority of the available resources are allocated to the actual production of fiber. Historically, the cleaning of polymer extrusion equipment received little attention and was relegated to the cheapest process available. However, as the complexity of capillary geometries of some of today’s spinnerettes has increased, precision cleaning has become more important and, at the same time, more difficult.

In cleaning spinnerettes or pack assemblies, a two-stage cleaning system is necessary. The first stage, known as precleaning, entails the removal of polymeric material or the reduction of this material to an ash. In many instances, this precleaning stage completely removes the polymeric materials. However, materials such as carbon residue or titanium dioxide are inert to the pyrolysis or volatilization process and must be removed by other methods. In the past, fine drills, broaches, or wires were used to remove this inert matter, but because of the damage caused to the spinnerette by using these methods, an alternative method had to be found. The use of ultrasonic systems is now the standard in the Fiber Industry.

The ultrasonic cleaner is a device in which thorough and powerful mechanical agitation is provided to a liquid bath. As in any device using mechanical and electrical motivation, there are elements of design which eliminate much of the guesswork and downtime. For example, ultrasonic cleaners have been designed to use magnetostrictive transducers rather than piezoelectric transducers to give more consistent results.

The ultrasonic cleaner, as its name implies, incorporates sound to accomplish its purpose. Sound waves, which are pressure waves, move through the bath and induce cavitation. It is the cavitation which produces a scrubbing action at the surface of the object being cleaned and releases energy in the order of 15,000 psi to loosen and lift dirt from hard to reach surfaces.

When an ultrasonic cleaner is initially energized with a fresh bath of aqueous cleaning solution, it first must expel the extraneous gases. This is called degassing, and bubbles not noticeable before will become large enough through agglomeration to become visible to the naked eye and, being buoyant, will rise to the surface. While this is taking place, and until it is completed, an action defined as gaseous cavitation is taking place.

Once the foreign gases are expelled from the liquid, vaporous cavitation occurs as vapor bubbles are compressed and actually imploded by the pressure waves. This cavitation, or minute vacuums, is capable of lifting surface dirt. It is believed that the shock, produced the instant of implosion, releases nuclei which, in turn, begin to form new vapor bubbles and therefore, provide for the action to repeat itself. Cavitation incidents are induced throughout the bath millions of times per second and provide an unequaled scrubbing action as long as sufficient energy is available. This last condition, "availability of sufficient energy," is one of a number of things which govern the success of an ultrasonic cleaning system. There have been many instances where ultrasonics failed, because, while it may have been able to perform at the time of purchase, one or more changes took place in the equipment or its operation which nullified the benefits originally realized from it.

Although there are many technologies used in manufacturing ultrasonic equipment, systems employing magnetostrictive, silver-brazed transducers tend to be extremely dependable while producing intense levels of cavitation. Systems that employ magnetostrictive transducers that are epoxy-bonded also produce intense levels of cavitation but run the risk of delamination due to impact or drastic temperature changes. After spending a considerable amount of research and actual cleaning trials, we have found that Lewis Corporation ultrasonics produces the best and most dependable ultrasonic cleaning system for the cleaning of extrusion equipment, and hence has become the Industry Standard.

Today’s state-of-the-art ultrasonic cleaning system too often has been construed to mean only the cleaning tank and its generator. These two items make up the cleaning equipment, but the term "system" must include the auxiliary equipment needed to yield clean parts or assemblies.

One important factor is a means to heat and filter the cleaning solution in the tank. This essential component will conserve the detergent and cleaning agents. The major purpose in having elevated and constant heat and maintaining a low level of contaminant in the ultrasonic bath is to enable the system, once established, to provide repeatable results in a production capacity.

A part is only as clean as the final rinse. Therefore, this important part of the system must be capable of performing a uniform and adequate rinsing of the workload after the ultrasonic wash has scrubbed and loosened the dirt.

To summarize, the following typical procedure is presented:

1. Precleaning, which as it implies, removes the gross contaminants before

putting the load into the ultrasonic cleaner. In the case of polymer extrusion hardware, this can be either ovens, fluidized beds, solvents, salt baths, or vacuum furnaces.

2. Final cleaning can be a multi-step process depending on the complexity of the capillary geometry as well as the level of contaminant left from the burn-off process. A typical extrusion final cleaning system involves the following steps:

A. Presoak - soak spinnerettes in an alkaline solution (JANED7025)

at 20% by volume at 180ºF. for approximately 30 minutes. This

stage loosens the contaminant for easy removal in ultrasonics.

B. Ultrasonically clean - clean spinnerettes in a Lewis ultrasonic

tank in an alkaline solution (JANED7025) at 10% by volume at

150ºF. to 160ºF. for approximately 30 minutes.

C. Pre-rinse - tap water rinse. Pre-rinse is necessary to remove

chemical residue from the part, preventing carryover to the

ultrasonic rinse.

D. Final rinse - ultrasonically or with air agitation, rinse the spinnerettes at 150ºF to 160ºF. tap or D.I. water for 10 to 20 minutes. This final rinse is one of the most critical stages in that it rinses the detergent and contaminant from the capillary.

NOTE: when complex geometries and small extrusion capillaries are present, an ultrasonic rinse is essential.

Other Factors that Affect Cleaning

Orientation - as critical as any element of cleaning spinnerettes or extrusion equipment, is the orientation of the part as it relates to the radiating surface of the ultrasonics. The most consistent results occur when parts are horizontal in a bottom mounted ultrasonic tank with the large open end (counter bore) facing the bottom of the tank. In other instances, parts racked vertically in a side mounted ultrasonic tank with the large capillary end (counter bore) facing the side mounted transducer are also effective. In either instance, it is important that all holes or capillaries have a direct, unblocked path to the radiating surface and are positioned within 4" - 5" from that radiating surface.

Consistent Cleaning Conditions - In order to ensure consistent cleaning results, it is imperative to maintain a consistent cleaning system.

A. Particulate Filtration removes buoyant particles suspended in solution that could otherwise redeposit in the critical areas.

B. Chemical Titration is necessary to ensure that the concentration of the cleaning solution is consistent.

C. Clean Rinse Water insures that the last water to touch the surface of the part does not redeposit previously cleaned soils.

D. Filtered Plant Air is critical when using air pressure to blow water out of the capillaries to facilitate drying. As you know, plant air is generally oily and full of foreign debris.