Expert Guide to Laundry Production: Extraction in the Laundry Industry

Water Absorption and Removal

At the end of the wash cycle each item in the load is saturated thoroughly with water. At this point the excess water must be removed from the load. Draining the washer only removes the free or surface water from these items but does not remove any of the water absorbed by the saturated fabrics. Cotton for example, can easily hold water up to 2.5 times its bone-dry weight. For example, 500 grams of dry cotton can absorb about 1.2 kilograms of water. Thus, the saturated weight of cotton is about 3.5 times the weight of bone-dry fabric.

Polyester fabrics absorbs less than 400 grams of water per kilo of bone dry; blends absorb varying amounts of water – 500 grams to 1 kilogram per kilogram depending on cotton content, fiber construction and weave.

This water is removed from the saturated fabrics mechanically and by evaporation. In laundry the term extraction always refers to the various mechanical methods used to remove moisture from fabric. Since it’s not possible to obtain 100% moisture removal by extraction, the remaining water must be removed by applying heat to textiles, and the residual moisture is evaporated. The evaporation process takes place in separate machines such as dryers, ironers and garment presses, tunnel finishers etc. The method of evaporation depends primarily on the type of classification of the item being processed. Typical laundry process systems and equipment always incorporates some type of extraction equipment for use in conjunction with dryers and or finishing equipment.

A properly designed and engineered extractor removes desirable quantities of water from saturated textiles as economically and as quickly as possible, reducing operating costs and increasing drying, ironing or finishing equipment productivity without adversely affecting quality.

Moisture Retention

Moisture retention is the weight of the water remaining in the fabric compared to the clean, dry weight of the fabric, and is expressed as a percentage. The formula for determining moisture retention is as follows.

% Moisture retention = Extracted weight – clean dry weight / clean dry weight X 100.

This equation is the actual weight of water left in the fabric.

The term dry can be interpreted in several ways.

• Bone dry = the textiles contain absolutely no moisture.

• Air dry = if bone dry items such as 100% cotton terry towels are left on the shelf in a humid environment, the goods will absorb some moisture from the atmosphere. This absorbed moisture is called regain.

• Acceptable dry = this is what the customer or end user will accept. Towels might feel dry and still have 8% moisture content.

Extraction Methods

Extraction is achieved by either of two basic methods – centrifugal force or compression force. Second Draft JUNE issue_18

Centrifugal force

When an object is rotated about an axis, an outward radial force – called centrifugal force – is exerted upon it.

The variable factors affecting moisture removal with all centrifugal extractors are:

• Type of fabric.

• Time.

• Centrifugal force.

• Loading factor.

• Chemical additives such as softener.

In the laundry industry centrifugal extractors are rated according to load capacity based on clean dry weight. These machines are designed to extract the maximum amount of water possible in the minimum amount of time.

Compression force

The other common mechanical method of removing water from saturated fabrics is by applying pressure to fabric and literally squeezing the water out of the fibers and fabric. Compression force is applied to the load by a hydraulically driven ram. The amount of water extracted depends on the total kilos of force exerted, the uniformity and effectiveness of this force in terms of kilos per square inch throughout the load and whether the outward flow of water is restricted in any way.

Continuous batch membrane extractors.

This type of extractor is fully automatic with continuous output of up to 40 batches per hour. Moisture content at this short cycle is about 70% on 100% cotton items and 35% on synthetic blends. The major problem is damage to buttons and fasteners etc on apparel.

Extractors: Advantages and Disadvantages

Selecting the best extractor for your laundry is not as simple as it may appear. After considering the more obvious factors such as cost and space requirements, a thorough and detailed analysis should be made taking into account many other factors.

• Determine the daily and hourly production requirements in kilos for each classification currently processed and for anticipated future tonnage.

• Determine for each classification the type of fabric, fiber, finish and washing process.

• Determine what must be done to the items after after extraction: condition, tumble dry, iron, press, tunnel finish etc.

With this information, consider the following basic design and operating characteristics of various extractors

• Extraction efficiency. This is the amount of water removed in a given amount of time.

• Productivity. This entails the number of loads or kilos produced per hour.

• Operating costs. These costs are expressed as per kilo processed and include: labor, electricity for pumps, drive motors and conveyors, water for pressure with membranes and diagrams and for cooling hydraulic systems, and compressed air for more moisture removal or air operated components.

• Reliability. This relates to breakdowns or malfunctions. For example, out of balance loads with centrifugal extractors, cake collapse or membrane punctures etc.

• Maintenance and repair. This cost includes the number of man hours required daily, weekly, annually for preventative maintenance as well as the frequency of replacement parts.