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Washing Equipment (the four generic types)

The miracle solvent appropriate for laundering is water. However, time, temperature, plus chemical and mechanical action are required to enhance the water's role by loosening the soil from the textiles and removing it by dilution. The amount of water used determines the amount of energy required to heat it to the required temperature. The vital component in the wash process is the type of washing machine used as this will determine the amount of water, energy and detergent used.

There are four generic types of  washing machines. They are top loaders, side loaders, washer-extractors and continuous batch machines. Top loaders are commercial machines such as those found in launderettes and are fitted with an agitator to provide the mechanical action (washing action). Side loaders and washer extractors are horizontally rotating washing machines with a cylindrical cage rotating within an outer case. The cylindrical cage is perforated to permit the wash and rinse liquors (liquor = water plus detergents and/or other chemicals) to pass in and out of the cage and so come into contact with the washing load. Lifters of various configurations are fitted or moulded within the cage to create the necessary mechanical action for aiding the loosening of the soil from the linen load. The majority of washer extractors have an access door at the end of the cylinder cage but some have a side access on the side of the cylinder cage. While these are side loaders, for the purpose of this report, these machines are all referred to as washer-extractors. What is referred to as side loaders in this report have no spin extraction facility and the wet load has to be transferred to a separate hydro extractor. In principle the side loaders are similar to the domestic twin tub machine while the washer-extractors are very much the same as the domestic type washer-extractor machines. Continuous batch washing machines (CBW's) are, as the name implies, machines that process washing on a continuous throughput of washing. These machines are described in more detail below.

With regard to efficiency in terms of water, energy and labour, side loaders are the least efficient and CBW machines the most efficient.

Where labour is plentiful but not necessarily efficient and where skilled maintenance is scarce, as is the case in many Third World situations, it may be expedient to use labour intensive side loader machines.

Table 5 compares the cost of side loaders and a CBW machine for a medium sized laundry in South Africa. This comparison illustrates dramatically the differences in water, energy and labour costs.  

Table 5: Cost comparisons between using existing side loaders and a new continuous batch washing system in a medium sized laundry (Feb 1993)

MACHINES

EXISTING EQUIPMENT

Proposed Equipment

Savings

Consumption

Costs/ Year

Consumption

Costs/ Year

Loading

None

None

1,0 kW/h

R430

R 430-

Washroom labour

15 persons

R 216 000

2 persons

R28 800

R 187 200

Washer(s)

20 kW/h

R 18 853

11,2 kW/h

R4 822

R 14 031

Extraction

21 kW/h

R 13 185

6,72 kW/h

R 2 893

R 10 292

Conveyors

None

None

0,50 kW/h

R 215

R 215-

Dryers

45 kW/h

R 42 379

6,72 kW/h

R9 042

R 33 337

Lint filter

None

None

0,50 kW/h

R 107

R 107-

Water

79 200 000 l

R 60 192

21,00 kW/h

R 16 050

R 44 142

Steam to wash

5 232 tons/y

R 235 440

0,25 kW/h

R 47 5200

R 187 920

Steam/ gas to dry

2 772 tons/y

R 124 740

21 118 000 l

R 86 688

R 38 052

Total

 

 

R 710 789

 

R 196 567

R 514 222

NOTE: Existing equipment has been calculated at 436 hours per month. New equipment has been calculated at 198 hours per month.

Prices:

Gas = R24 per GJ (GigaJoule)

Electricity = R0,18 per kW/h        

Capacity 220 000 kg/month = 1,111 kg/hour

Steam = R45 per ton                    

Capacity of new equipment  = 1,375 kg/h

Personnel = R14 400 per year

The capital cost of the proposed equipment has been excluded but the capital costs would be recovered from the savings within 3 years.  

Side loading machines with no built-in hydro extraction

The washing is taken out (usually manually) dripping wet from the machine, placed into trollies and hand loaded into hydro extractors. From there the washing is loaded into hydro extractors. From there the washing is loaded into trollies and either tumbled dried or transported to the flatbed ironers or laundry presses. The machines are reliable, unsophisticated and can take a lot of abuse. Few of these machines are used for Third World situations. They are referred to, affectionately by some, as the "donkeys" of the industry and by others as antiquated. They are the most labour, energy, water and space consuming machines when compared to washer-extractors and CBW machines but require the minimum of skilled maintenance. They are generally used in medium sized laundries. They are available in models ranging from 2-140 kg dry weight per machine. These machines are manufactured in the RSA, USA and Far East and heated by steam or electricity. See Figure 1 for an isometric sketch of a side-loading machine.

Figure 1 Isometric sketch of side loading washing machine.

Washer extractor machines

There are many models available which differ greatly in sophistication from rigidly mounted machines to others mounted on "hydro cushions" to obviate vibration. For the non cushion type machines, vibration can be a problem if these machines are mounted on floors above ground level. The various models take from 10-300kg dry weight of washing per machine. As the name implies most  of the washing from these machines does not require further hydro extracting. Flat work can generally be taken directly to drying ironers - uniforms, shirts, etc. would normally be tumble dried prior to pressing and towels, etc. would be tumble dried ready for folding.

For convenience in this report washer-extractors have been divided into four basic types:

  • normal spin producing 80-90G
  • medium spin producing 135-150G
  • high spin producing 200-250G
  • super high spin producing ±350G

The spin referred to above is the final spin of the machines and the breakdown is fairly arbitrary.

The efficiency of hydro extraction is most effective from 100-200G. Above 200G the amount of water extracted is more gradual. Figure 2 illustrates the extract efficiency of the G Force on the percentage of water retention for cotton, poly-cottons and terry towels. From this it can be seen that water retention in cotton goods decreases from 100% to 62% at 200G and to about 53% at 400G.

The normal, medium and high speed spin machines are used most frequently in South Africa. The trend in Europe and the Far East is for super high spin washer-extractors that are free standing and can be installed above ground level, which gives total flexibility in positioning them. Further, these machines can be installed with water re-use tanks, for greater water and effluent efficiency. These machines are available locally but cost considerably more than fixed machines.

Figure 2: Extract efficiency of "G" Force on the percentage of water retention in various textiles.

Most washer-extractor machines are available with or without water recovery mechanisms. For example, a washer-extractor with no water recovery would use 20 - 25l water/kg work whereas one with a single water recovery would use 15 - 20l water/kg work and one with a double water recovery would use only 12 - 17l water/kg work. The most cost-effective schemes for water economy normally involve integration of heat and water recovery.

Machines are available that are pre-programmed for specific laundry types such as hotels, motels, health care institutions, shirt laundries, commercial laundries, restaurants, etc. In addition machines are also available with large variety of built-in programmes that can be chosen with the press of a button.

Washer-extractors are used in small coin operated laundrettes up to medium to fairly large laundries. They are the most popular and generally the only choice for small to medium sized laundries in all First World countries. They consume less labour, energy, water and space than side loading machines but require more sophisticated maintenance skills than side loaders.

In the USA, as in South Africa, many institutions, especially hotels and motels with in-house laundries, use poly-cottons for sheets and pillow cases. These are the "wash and wear" type. The items are tumble dried, folded and placed directly on the bed. Washer-extractors are used for the laundering process. Some of these machines are programmed with a cool-down facility for poly-cottons and care must be taken in the choice of machines for 100% cotton, which is a popular choice for local hospitals. Aspects to look at are the gradual temperature changes necessary for poly-cottons from the hot wash to the cold rinse and the lower spin speeds - especially in some of the larger machines that take 30kg dry weight or more. Machines that allow for re-programming do not constitute a problem.

In the hotel /motel industry, where poly-cottons are used, sheets, etc are sometimes ironed to ensure a good appearance. This defeats the whole concept of the use of poly-cottons and indicates poor washing and drying processes. (See also para 1.6)

The industrial machines use either steam or electricity for heating. See figure 3 for an isometric sketch of a washer-extractor.

Figure 3 Isometric sketch of washer extractor washing machine.

Continuous batch washing machines (CBW) (See also Appendix C)

These machines are only considered for large laundries (600 kg dry weight washing per hour or more.) As the name implies, the washing can be separated by textile compatibility into batches with a continuous throughput of washing producing clean dry washing from the soiled state to the dry clean product at pre-determined batch intervals. A tunnel washer does not just replace a line of batch washers, it must be regarded as the core of a wash system. The installation of a tunnel washer should dictate the end of 'ad hoc' planning of production through the laundry.

The main differences between a CBW machine and a washer-extractor are as follows:

  • In a CBW machine the linen moves through the unit from one separate compartment to the next. It spends the same times in each compartment, undergoing a succession of specific treatments, which together make up the total laundering process.

  • The water and detergent/ chemical (liquor) movement is mainly contra-flow to that of the work, flowing from compartment to compartment.

  • It is possible to control accurately the temperature, chemicals concentration and dip level in most compartments. The design of the wash process for an existing CBW machine thus requires a detailed knowledge of the machine being used.

The forerunner of these machines is the Archimedean Screw type. This type has small washing compartments with a bottom transfer of water and at the time of writing this was the type generally in use locally - mostly at Provincial central laundries. In general terms the interior of a tunnel cage is designed as an Archimedean Screw, each section holding a batch of work. Normal wash movement of the screw retains the work in its position but a 360° forward turn of the screw moves the work forward to the next stage of processing.

The tube or tunnel cage is therefore divided into processing sections which conform to pre-wash, hot-wash and rinse zones, the work moving from pre-wash through the machine and out after rinsing.

Movement of work is from the load end of the machine to the discharge point.

Water flow is from the discharge point to the load end of the machine.

A competitor on the market is the batch washer with larger compartments with a top transfer of water. This type of machine has sealed water compartments which allows modules to be added to increase capacity.

There are a number of different modules available. They are sophisticated with fully automated washing transport systems and programmable chemical, water and timing control systems. They are capital intensive but if properly maintained and managed are the most economical in terms of labour, space, energy and water. Regarding economical use of water, for example, a CBW machine will use 7-10 l water/kg of work compared to a washer-extractor with a double water recovery system which would use 12-17 l water/kg of work. To assist in a better understanding of these machines see Appendix C.

These machines only operate with steam and as with the side loaders and washer-extractors that use steam, the cost of steam generation (either existing or new) has to be added to total cost. Steam is generally the best energy source for the large laundry that uses either washer extractors or CBW machines. The smaller on-site laundries generally use electrical water heating unless there is a steam generating plant on the site, such as a hospital, using steam for other purposes. (see also para 15.3).

Productive output per hour is the key to most purchasing decisions in the laundry. It is perhaps more critical in the case of a CBW machine because of its high capital cost. This capital investment must enable the launderer to achieve a considerable increase in output, together with other savings in running costs. How does one determine the number of compartments? Brown states that two exercises need to be carried out:

  • Determine the throughput required in dry weight/ hour.

  • Determine the wash process required within the machine to determine the number of sections.

The first part is obvious but the second, according to Brown, is not as simple as the systems must be planned and designed to process the most difficult or most heavily soiled work. If this is a small portion of the linen to be laundered, then a dedicated washer-extractor(s) could be used for this work.

The problem of determining the wash process required within the machine is briefly addressed in Appendix C. At the early briefing stage clients and designers should consult with experienced laundry consultants in this regard. Brown states: "Get the process specification correct first, then look at comparative steam, water and chemical usage and don't over-complicate requirements. Then look for the simplest, easiest way of meeting your demands. The more complex the system, the more problems you will get."

See Figure 4 for an isometric layout for a CBW system.

As stated in para 3.3, it is strongly recommended that "infected" work is not processed through a CBW machine. This work should be processed through a dedicated washer-extractor.


This information courtesy of Division of Building Technology, CSIR.


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