Last updated on August 8th, 2023 at 11:40 am
Definition and General Remarks of Dry Cleaning
Dry cleaning can be defined as the cleaning of fabrics in a substantially non-aqueous liquid medium. This process has evolved during the last 75-80 years into a high effective, low cost, safe method of removing soils from all types of textiles.
There is a clear record as to when the process began. The first dry-cleaning business was established by a Frenchman, Jean Baptist Jolly in 1825. Solvent cleaning was introduced in Perth, Scotland in 1866 and dry-cleaning began to be used extensively in the U.S.A. in the period 1910 – 1920. This industry developed as a result of the large scale production of gasoline. Gasoline was the major dry-cleaning solvent until 1928 when less flammable odor free solvent was developed known as Stoddard solvent in recognition of the work of W.J. Stoddard. The industry enjoyed a steady growth until the introduction of wash-and-wear garments and after a period of adjustment again began to expand and diversify.
The original dry solvent technique removed oil-soluble stains. Current methods remove oil, many water-soluble and some insoluble materials with the help of detergents and various agents. The important distinction between dry and wet solvents is that the latter swell the hydrophilic textile fabrics while dry solvents do not. Dimensional changes that fibres undergo as they swell can cause fabric shrinkage, wrinkles, and color bleeding. Dry-cleaning solvents do not cause fibre swelling and so do not cause shrinkage, wrinkles, and color bleeding. Also oily stains are removed at low temperatures in dry-cleaning while in laundering high temperatures are needed. Hence dry-cleaning is a safe method for cleaning delicate textiles. Fabrics sensitive to wet treatments can be cleaned effectively of oily stains by dry-cleaning.
Both laundering and dry-cleaning remove soil by the same mechanisms and similar operations. Garments are tumbled in the cleaning liquid in horizontal washers. Detergents are used in both cases to emulsify or solubilize the soils insoluble in cleaning liquid. In laundering bleaching agents are added and strong alkalis can be used to saponify fats. Saponification is not used in dry-cleaning but techniques have been developed to permit the use of some bleach in dry-cleaning.
Dry Cleaning Process or Operation
A number of processes are involved in the dry-cleaning operation. These processes are explained in detail below –
When the solid garments are delivered at the laundry, they are first sent to the marking department. Here a tag, a white piece of fabric with a number or some other code stamped on it with indelible marking ink, is securely attached to the garment. Each article is treated individually to facilitate identification.
The garments then pass on to the sorting department. At this point if there are any tears or seams that have ripped open the garment is sent to the seamstress for mending. Various types of garments are sorted out into different hampers so that each hamper contains only one class of garments and can hold a lead of about 45 kg. There are six major groups into which the cloths are sorted. These are –
- White and light colored cloths.
- Dark colored cloths.
- White and light colored woolens.
- Dark colored woolens.
- Draperies and furniture covers.
- Raincoats and windcheaters.
At this stage pockets are checked and cleaned and other parts of the garment showing dust or dirt are brushed and fancy buttons, buckles etc. are removed.
Heavy soiled areas of the garment are treated with solvents. Volatile dry solvents like amyl acetate are applied to remove oil-borne stains while non-volatile solvents are used on paint and varnish stains. Water soluble stains such as perspiration are spotted with emulsifying agents (water and solvent mixed together). Some pre-spotters are digestive agents. They are mixtures of enzymes capable of digesting food stains. Pre-spotters are applied using a spotting gun which uses compressed air and helps spray the solvent on to the stain or heavily soiled area. Special spotting tables are equipped with steam guns, compresses air and spot removal chemicals. All chemicals used are removed.
The workload of approximately 45kg is transferred to the dry-cleaning cylinder. Very delicate cloths are put in a net bag. Appropriate solvent is circulated through the cloths. The contact time of the cloths with the solvent and the rinse time vary according to the rate of flow of the solvent and the size and type of the workload. This can vary from 5 to 45 minutes depending on fabric consumption and degree of soiling. The dry-cleaning machine is constructed in such a way as to provide mechanical agitation of the work-load. The horizontal drum has ribs built in to help lift up the garments as the drum rotates. These garments then drop back into the solvent. Thus immersion and agitation of the garments in the solvent takes place, loosening the soil and dissolving it out. The drum is also perforated to allow the solvent to flow through.
The excess solvent is removed from the garments by centrifugation or in a revolving perforated cylinder contained in a tumbler. Modern dry-cleaning machines perform the cleaning and the extraction in the same cylinder. The operators are not exposed to solvent vapors. In the older dry-cleaning drums using petroleum a separate extractor was used.
After extraction of excess solvents, the garments are dried in a drier which is a perforated drum enclosed in a tumbler. Hot air is passed through the cloths and is sucked out by an exhaust fan. The temperature is controlled to around 700C. Garments that might be damaged by tumblers are dried in a drying cabinet in which there is a fan.
Filtering and Distillation of The Solvent
Solvents are expensive and therefore filtered, distilled and re-used. They are not allowed to evaporate into the atmosphere. This also reduces the fire hazard and health hazard to workers in the laundry. Dry-cleaning solvents are purified by two processes:
- Filtration: The first filter is a mechanical one which holds back all solids such as dust, dirt particles, and lint. The solvent then passes through a filter of activated carbon or diatomaceous earth which clears the color of the solvent and also removes all greases, waxes and water.
- Distillation: The solvent is heated to its boiling point in an enclosed system. It evaporates, passes through condensers and the pure solvent is obtained. Oily and greasy soils which were dissolved by the solvent during the cleaning process remain behind and are removed. All traces of color, detergents and remaining water are removed at this stage.
Dried garments are inspected to check that they are perfectly clean. If necessary they are spot cleaned a second time. Wet cleaning may at times be carried out at this stage. In this operation each item is inspected individually. If any spots or stains are seen; the garment is sent back to the spotting department for their removal. The spotter has to passes a good knowledge of textiles fibres, fabric construction, dyes and chemicals. He should also have special skills and knowledge of techniques to be used. This will help him to know which stains can be removed without damage to the fabric and how to do this.
In this process the garment is restored, as near as possible, to its original size, shape, feel and appearance. The extent to which this is possible depends on the quality of the fabric, the dyes used and the quality of tailoring.
Clean garments are pressed. This can be done on steam air forms which are of various styles or by finishing presses which are of two basic types; the grid head press used on woolens and the hot head press for silk and silk like fabrics. Both these types of presses have perforated bucks as the bottom plate. The grid head press has a perforated head, while the hot head press is smooth and non porous. The heads are heated internally by steam to a surface temperature of 1490C. The garment is placed on the buck and pressure is exerted by lowering the head.
Proper use of these presses is a skilled art. Pressing is the most expensive operation in dry-cleaning.
Many dry-cleaners provide special services. Besides garment repair, they also offer re-dyeing, water proofing, moth proofing, softener application, sizing etc. They also clean leather.
Dyeing and application of finishes like water-proofing, moth-proofing, anti-static finish application etc. are each done in separate departments.
Buttons and buckles that had been removed are stitched back. Finally the garments are packed in paper or suspended from cloth hangers, covered with polyethylene bags and are ready for delivery.