The recommended machine capacity is given by dry weight.The formula to calculate the correct weight ratio for fabrics and drum diameter: the Degree of Loading (DoL) that is the weight of work/volume of the machine cage relationship.
Volume of a cylinder
Cage volume = πr2L
Where π = 3.142
r = radius (cm)
L = length (cm)
This calculation gives the volume of the machine cage in cubic centimetres.
To convert to litres divide by 1000. For example,
For a cylinder with a radius of 90cm and a length of 40cm –
Volume = 3.142 x 90 x 90 x 40 = 1018L
The DoL is normally expressed as gm/lt and experience across the industry indicates that a range of between 45-90gm/L will provide an acceptable DoL for most types of laundry work.
Normally Washer Extractor capacity is calculated by drum volume /10.
That is Filling factor = 1:10 and Dryer = 1:20.
For example: 1000lt drum volume will have around 100kg capacity and dryer 50kg capacity.
In a 60kg Washer with Hard mount machine and a 50kg Dryer, the load filling capacity differ. You can load 50kg linen but the Drying time is a bit longer unlike in the soft mount machine.
Another determining feature is the G-factor of the washer.
Hard mount G factor 100-300 which depends on the make and design
Soft mount G factor 300-425 G
Things that need to be considered while calculating the load include: volume of the washer drum, ratio between the diameter and depth of drum, the percentage of perforation &drum metal thickness and the gap between wash tub &outer drum. DoL differs for all textile items – GSM-weight, size, textile type.
Since towels absorb more water, per kg of loading space requirement is the highest. There are no fixed formulas for establishing how much per cent of one particular item can be loaded in one particular capacity of machine.This is usually established by the laundry operator after a few trials, taking into consideration the consumption levels of chemical, water, time and temperature. This helps in establishing productivity vis-à-vis production costs.
While the international standard for washer extractors is 1:10; that is for every dry kg of linen there has to be 10lt of volume(space) available, some manufacturers also calculate by taking 1:9 and 1:11 ratios depending on the different laundry needs but the volume remains the same.
Dryers, on the other hand, with the same capacity of 50kg will have two drum ratios – 1:20 and 1:25. For example,dryers in 1:20 ratio will have 1000lt volume and 1:25 ratio will have 1250lt volume.
Firstly, dryers in 1:25 ratio have 25% higher drum volume and secondly, in the heat transfer machine, majority heat is wasted by way of exhaust. So by having faster and better heat transfer ratios, one can always reduce energy consumption per kg of drying. The question that arises is that why does a dryer have two ratios for the same capacity of washer with a 1:10 ratio?
The amount of textile fed into the dryer with 50% residual moisture will weigh 1.5 times more than what it was at the time of washing. Drying would require larger textile surface area.If you keep the bundled textile in the open, it will take much longer time to dry compared to a spread out textile piece.In short, more space allows more area for textile to breath in a dryer and similarly, more &faster heat transfer, results in faster drying, leading to overall reduction in energy consumption per kg of linen.
The High-G force must come with options of flexible controls so that the laundry operator can control residual moisture depending on textile type.This will not only reduce cost of production, but also enhance textile life.
Also with High G force, one must take into account the relative performances of each machine in different process category to ensure equilibrium in laundry. Otherwise, you will end up either with bottle necks or underutilized capacities leading to higher operating costs.
These issues need to be addressed specifically for each laundry requirement and though there can be a generic impression, one must not depend on it entirely while planning machines
Halilur Rahman
Formula to calculate Residual moisture
Wet Weight of linen-Dry weight of linen X 100
= Residual moisture in %
Dry weight of linen X 100
Wet weight is the weight of the linen after extraction
Dry weight is the weight of the linen after tumble drying
Filling factor drying
Cotton, terry towels
1/22 or 1/25 1 kg of load for every 22 or 25 litres of drum volume
Synthetics and blended fabrics
1/50 or 1/60 1kg load for 50 or 60 litres drum volume
Filling the tumble dryer correctly
Filling the dryer is not about fitting as much as possible the drum. The maximum load is 1 kg of garments for every 18 litres of drum volume for a 100% cotton load. Depending of the size and type of garments, it can be an advantage to use 1:25 or lower (e.g.1:33 for mixed blends).
With Soft Mounted washers
40% of the total washing capacity will be dried
Dryers will take roughly 30 min (2 cycles/h) to process the linen
With Hard Mounted washers
40% of the total washing capacity will be dried
20% of the total washing capacity will be pre-dried before finishing
Dryers will take roughly 45 min (1,5 cycles/h) to full-dry the linen
Dryers will take roughly 20 min (3 cycles/h) to pre-dry the linen
Formula to calculate the G-factor
G-Force is a relative measurement used to compare a washer’s extraction capabilities (spin cycle). Comparatively, higher RPM’s relate to higher G-Force when the cylinder size is similar. However, larger diameter cylinders can spin slower, yet attain a higher G-Force than smaller diameter cylinders.
Formula
rpm2 x d(m) / 1790
- rpm = drum rpm
- d = drum diameter in meter
- 1790 = constant