GB2051883A

GB2051883A - Method of and a machine for washing laundry

Info

Publication number: GB2051883A
Application number: GB8015663A
Authority: GB
Original assignee: Hoesch Werke AG
Current assignee: Hoesch Werke AG
Priority date: 1979-05-12
Filing date: 1980-05-12
Publication date: 1981-01-21
Also published as: BE884711A; GB2051883B

Description

SPECIFICATION Method of, and a Machine for. Washing Laundry The invention relates to a method of washing laundry and to a washing machine, and in particular to a method utilising a washing machine having a perforated drum rotatably mounted about a horizontal axis in a casing. In such a machine, the laundry is, during washing and rinsing actions, repeatedly lifted by the drum and then allowed to fall on to the lower part of the drum. Then, by gradually increasing the drum speed, the laundry is distributed fairly evenly on the drum wall, and is centrifuged on further increase of speed. Known washing methods have a relatively long washing and rinsing periods, and use large amounts of liquid (water and detergent mixtures). One of the greatest problems of these methods is the achievement of an adequate exchange between free and bound liquid. In the first place, the liquid contained in folds of the laundry articles, and between the threads of the laundry material, flows away. Moreover, exchange between liquid adhering to the surfaces of the individual laundry fibres, and that filling the interspaces between the fibres, takes place only inertly, and in most cases inadequately. The large amounts of liquid used results in a high water consumption, and the heating of these large amounts of liquid requires a corresponding large energy consumption. In the case of problem laundry, for example geriatric or miner's laundry, which often contains dirt proportions of 50% or more of the basic weight of the laundry, several washing actions and correspondingly many more rinsing actions are necessary. The aim of the invention is to provide a method which, even in the case of problem laundry, requires only one washing action, so that the water and energy consumption are kept to a minimum. Surprisingly, this aim is achieved by using only a quantity of washing liquor sufficient to wet the laundry. Accordingly, the present invention provides a method of washing laundry in a washing machine having a generally cylindrical, perforated drum rotatably mounted about a substantially horizontal axis in a casing, the method comprising the steps of introducing washing liquor into the casing until the washing liquor just covers the bottom of the inner cylindrical surface of the drum, introducing articles of dry laundry singly into the drum, rotating the drum at a speed which generates a centrifugal acceleration of between 0.3 g and 0.8 g at the drum circumference thereby uniformly wetting the laundry, increasing the drum speed so as to generate a centrifugal acceleration of slightly less than 1 g at the drum circumference,and maintaining this drum speed for a predetermined time in order to wash the laundry. Advantageously, the method further comprises the steps of increasing the speed of rotation of the drum to a spin-drying speed, the transition to spin-drying speed being effected gradually, of reducing the speed of rotation of the drum from the spin-drying speed to that at which the laundry was introduced into the drum, and then of rinsing and spinning the laundry at least once after said speed reduction of the drum, the or each rinsing action comprising the steps of introducing water into the casing and increasing the rotation of the drum to a speed which generates a centrifugal acceleration of slightly less than 1 g at the drum circumference, a spinning action following the or each rinsing action,the or each spinning action being effected by gradually increasing the speed of rotation of the drum to a spin-drying speed. Conveniently, the wetting of the laundry is effected using a quantity of washing liquor sufficient only to give the laundry a pasty consistency, said quantity of washing liquor corresponding to about 30-70% of the absorption capacity of the laundry. It is expedient to proceed in such a manner that the washing liquor level in the drum is maintained until the predetermined degree of wetting is achieved. Preferably, this is effected by using a quantity of washing liquor such that the height of the level of the washing liquor in the drum is 5% of the drum diameter. To achieve a uniform wetting of the laundry, the washing liquor level may be increased to about 10% of the drum diameter, the additional liquid being water. Advantageously, the washing liquor is a concentrated washing liquor. In this case the washing liquor may be a saturated washing liquor which may have a solid phase present. Preferably, after the uniform wetting of the laundry, washing is effected at a drum speed which generates a centrifugal acceleration of substantially 0.8 to 0.95 g. at the drum circumference. In the subsequent transition to spin-drying speed, the increase of the drum speed, in the range between washing speed and about 2 g, may be controlled in dependence upon any imbalance of the laundry in the drum. In this case, upon an imbalance occurring, the drum speed is reduced to less than 1 g, after which the drum is re-accelerated. Advantageously, spin-drying is effected with a drum speed which generates a centrifugal acceleration of between 3 and 350 g at the drum circumference. At the end of the spin-drying action, rinsing water can be admitted into the housing, the rinsing water being introduced between the casing and the drum in a quantity such that a considerable back pressure is generated. Irrespective of the degree of soiling of the laundry, washing will be effected in one washing action and one, two, or three rinsing actions. Preferably, the temperature of the rinsing water does not exceed, and differs little from, the temperature of the washing liquor. Preferably, a washing liquor containing detergents will be used, and/or detergents will be added to the rinsing water. The invention also provides a washing machine having a generally cylindrical, perforated drum rotatably mounted about a substantially horizontal axis in a casing, a liquid level sensor for sensing the level of liquid in the drum, a programme control system, and a device for controlling the rotational speed of the drum, said device comprising a vibration sensor which is connected to the programme control system and the motor through a comparator circuit, and wherein the motor is provided with a tachometer which is attached to the comparator circuit. Preferably, the drum has a loading opening at one end and a discharge opening at the other end, said openings being concentric with the drum axis, the diameter of the discharge opening being larger than 120 millimetres. Advantageously, the drum is pivotably mounted within the casing. The loading opening may be formed as a hollow frustoconical shaft whose wider end is rigidly attached to the drum. In this case, the drum may be mounted in the casing by means of the hollow shaft, and the hollow shaft may be supported in the casing by means of a hydrostatic bearing. Advantageously, a chute is provided for directing laundry into the loading opening, means being provided for pivoting the chute away from the loading opening. Preferably, a gap is situated between the drum and the casing, the gap being of tapered crosssection. Advantageously, the tapering gap results from an eccentric arrangement of the drum in the casing. The drum may have a diameter of between 800 and 2000 millimetres, and preferably has no carrier fins. In contrast with known washing methods, in which free washing liquor must be present in addition to the liquor absorbed by the laundry (a liquid level of at least 20% of the drum diameter being regarded as normal), it has surprisingly been found that this high proportion of bound and free liquid in the drum is not necessary. On the contrary; it is advantageous to reduce the proportion of bound liquid decisively. This is, however, possible only if the laundry is introduced into the drum in a dry condition, and is uniformly wetted with prepared washing liquor. This means that the washing liquor must already be present in the desired concentration in the washing machine when the laundry is introduced. Alternatively, the washing liquor must be introduced into the washing machine simultaneously with the laundry.Attention is to be given here to a wetting of the washing which, while moderate, is as uniform as possible. In this case, for example, 10 kilograms of dry laundry, less than 6 kilograms of concentrated washing liquor needs to be introduced, that is to say the laundry can have a degree of moistness which lies only a little above that which laundry possesses normally after a spin-drying operation. However, in many cases a higher degree of wetting will be preferred. For example, according to the textile material and the type of weave, up to about 2 litres of liquor for 1 kilogram of dry laundry can be used. The correct degree of wetting of the laundry may be seen from its "pasty" consistency. This means that a heap of laundry thus wetted must possess a certain resilience, and give off to its carrying surface moisture only in the form of a thin film of liquid.In other words, no water drips or flows out of the laundry even when stored for a lengthy time. Although the theory behind the washing method of the invention is not fully understood, it is assumed that only so much washing liquor need be present that the interspaces, present between the fibres of the textile threads of the material of the laundry, can be filled, and that the surface of these fibres must be wetted as completely as possible. Since dirt particles can be present at all these points, they must also be wetted with washing liquor. This is both necessary, and adequate, for effective washing. This is achieved, in accordance with the invention, by introducing the laundry articles singly during wetting, and by maintaining a low liquid level in the drum whilst rotating the drum at a speed which avoids tangling of the laundry, but which distributes the laundry approximately evenly within the drum. This speed is also dependent upon the material of the laundry, and lies approximately in a range at which a centrifugal acceleration between 0.3 and 0.8 g is generated at the drum wall. Thus, the theoretically necessary quantity of washing liquor is very small. In practice, a certain excess is utilised, since the water contained in the liquor also acts as a transport medium for the detached dirt. Since the drum is already in motion during the wetting operation, the individual laundry articles are lifted to a certain height, and permitted to drop in a parabola on to the lower part of the drum. At the indicated speed, the laundry articles do not reach the top of the inside of the drum, so that they do not fall too far, and so strike the drum wall in such a manner that the laundry gives off relatively little liquid, but can absorb additional washing liquor from the free liquid in the drum. On the other hand, the speed is high enough for the liquor level to lie obliquely within the drum, so that no free liquid is present at the point of impact of the laundry. Since the laundry is introduced dry, rapid and uniform wetting is possible. If the inter-fibre cavities, which are important for the washing action according to the method of the invention, are already occupied by water (for example due to prior soaking, or due to the introduction of water into the drum with subsequent liquor production), homogeneous wetting could no longer take place, since it is extremely difficult to achieve an equalisation of the liquor concentration in a short time in this region. If however, liquor is introduced from the outset, it is only necessary for careful wetting of all cavities to take place due to the mechanical work. Even at this stage of the method, a part of the dirt is delivered to the free liquid, that is to say the washing action has already begun. In the subsequent increase of speed to a speed which generates a centrifugal acceleration of between 0.8 and 0.95 g at the drum wall, the mechanical working is continued, and the laundry articles are carried higher before they drop. The exchange between free and bound liquid is thereby made more intensive. Before, or during, this method step, the liquor level in the drum can be raised to about double the previous level, so that it amounts to up to about 10% of the drum diameter. Since the higher speed intensifies the oblique positioning of the liquor surface level, and increases the exchange between bound and free liquid, the actions in the drum do not change fundamentally, but merely experience an increase of intensity.However, the addition of free liquid effects an increase in quantity of the total liquid mixture, and of its absorption capacity for the detached dirt. Such an addition of free liquid can, therefore, be expedient in the case of heavily soiled laundry. However, there should not be so much free liquid in the drum that the laundry falls not on to the drum wall but on to the liquor. Since it is sought to wash even problem laundry, such as geriatric laundry and industrial laundry, in a single washing action, a washing liquor should be used into which the entire quantity of washing agent necessary is charged. In the case of heavily soiled laundry, this can be a concentrated or even saturated washing liquor having a solid phase. In the case of the mentioned "pasty" consistency of the laundry, carrier fins in the drum are not necessary. Since considerably higher spindrying speeds are expedient for the method, a drum having no carrier fins is advantageous for the avoidance of imbalance. The spin-drying action is initiated by the evacuation of the soiled free liquid. Then, the drum speed is increased gradually so that distribution of the laundry in the drum takes place without imbalance. Preferably, the increase of the drum speed takes place in dependence upon any imbalance, in such manner that the rotational speed is increased in proportion to the reduction of the imbalance. In this way, success is achieved in passing through the critical range directly below 1 g, in which the laundry is applied to the drum walls, in such a way that a wobble-free highspeed running is achieved, on account of completely uniform distribution of the laundry. The removal of the liquor from the inter-fibre zone is more difficult than the removal of the liquor contained between the individual textile threads, and in folds of the laundry. For this purpose, as a rule, higher speeds are necessary. The magnitude of these higher speeds are dependent, however, upon the materials of the laundry. A reduction of the centrifuging speed is achieved in that the laundry is treated with hot liquor and/or hot rinsing water. Hot rinsing water not only detaches the remaining liquor from the pores and capillaries more easily and more rapidly, but also can be centrifuged more easily out of the laundry. This is because hot water has a lower viscosity than cold water, and so does not adhere so firmly in the capillaries and pores of the laundry. This effect is reinforced many times by the fact that the laundry is treated with hot rinsing water containing some detergents. A sufficient quantity of detergents is always present in the rinsing water, because detergents added during the washing process are entrained in a sufficient quantity even into the last rinsing process.Thus, the hot detergent-containing rinsing water has the advantage that lower spin-drying rotation speeds suffice for the removal of the bound liquid. Of course, the method according to the invention can also be used with relatively cold water for heat-sensitive laundry. Then higher spin-drying speeds of rotation must be used. As mentioned above, the necessary spin-drying speeds are dependent upon the laundry material. Thus in the case of polyester goods, satisfactory results can be achieved with a spin-drying speed of about 3 g, as is generally usual hitherto. For heavy cotton goods, on the other hand, spindrying speeds of 250 to 350 g are necessary. With these high spin-drying speeds, special care must be applied to the distribution of the laundry to prevent imbalance. Nevertheless, if an imbalance occurs, a correction is possible only by returning to a speed of below 1 g, and then reaccelerating. At a speed of 2 g, the laundry distribution is completed, and acceleration can be effected further as desired. At the end of the spin-drying action, the drum must be braked. According to the invention, this is effected by introducing water into the casing. The quantity of water introduced into the casing is such that the water comes into contact with the drum, and is carried by it, while a considerable back-pressure occurs in the interspace between the casing and the drum. Intense turbulence of the water occurs, which can be used to rinse away dirt which has settled in the casing, and externally on the drum. A further effect of the braking water, is that the laundry, which is pressed firmly against the drum wall by the considerable centrifugal acceleration, and which normally can be detached only with difficulty from the drum wall, is forced away from the drum wall by the back pressure of the water. The washing action is followed by at least one rinsing action which proceeds in a similar manner to the washing action. This means that the laundry is firstly distributed at 0.3 to 0.8 g in the drum, acceleration is effected up to 0.95 g, and spin-drying is effected after at least partial evacuation of the rinsing water. Three rinsing actions are sufficient even for problem laundry. Since the exchange of liquor residues in the capillary range is a problem, rinsing takes longer than washing. Over-wetting of the laundry here again leads to entraining of quantities of water, the effectiveness of which is out of proportion to the energy required for their movement. The exchange between bound and free liquid is achieved, not so much by liquor washing action as by mechanical drum work.In this context, the drum must be of a certain size, in order to achieve an adequate speed of drop of the laundry. Thus, the minimum diameter should be 800 millimetres, as below this diameter the effectiveness falls off very rapidly. A maximum size can likewise be stated, namely a diameter of 2000 millimetres. While larger drums can revolve at a lower angular speed, the number of dropping actions per piece of laundry, and per unit of time, is lower. These dropping actions, however, must not fall short of a certain minimum number per piece of laundry, even in the case of an increase height of drop. The spinning actions which occur after the washing action and between the rinsing actions do not need to be carried out at the maximum speed. Thus, for example, in place of a speed of 250 g, a speed of 80 can be used for these intermediate spinning actions. Thus, a part of the washing liquor (and of the detergents contained therein) can be deliberately entrained into the next rinsing action. The degree of water extraction is further dependent upon the spinning time. It is advisable for the final spinning action to take longer than the intermediate spinning actions. Here it should be noted that a bath ratio of at least 1:2 should be used for the washing action, a bath ratio of 1:3.5 for the intermediate rinsing actions, and a bath ratio of 1 :4 for the final rinsing action. This is achieved in that the casing part situated beneath the drum, that is the liquor or rinsing water tank, is made correspondingly large. The water saving is thus largely achieved, not by smaller amounts of liquid, but rather by reduction of the number of washing and rinsing actions. Furthermore, an energy saving is achieved by short working times. These have the further advantage that only a little moisture penetrates into the textile fibres, and causes them to swell. Excessive swelling constricts the inter-fibre spaces, and permits entry of less liquor, which decisively reduces the effectiveness of the washing action. For this reason, prior wetting or soaking of the laundry is disadvantageous. A further essential advantage of this method is that the laundry can be handled considerably more gently. The following example illustrates the invention. Example 10 kilograms of washing agent were dissolved in 280 litres of water at 95[deg]C, and introduced into a washing machine having a drum volume of 2000 litres, until a liquid mixture level of 6 centimetres was reached in the drum. Then, 170 kilograms of industrial laundry, consisting of work-suits and underclothing from a foundry, the laundry having an average degree of soiling of 15-20% of its basic weight, was introduced into the drum, the liquid mixture level being maintained until the whole of the laundry was introduced. The items of laundry were introduced into the drum one by one. During this operation the drum was rotated at a speed of 28 r.p.m., and this rotation was continued after the introduction of the laundry was completed. This operation (the wetting operation) took five minutes.Then a further 315 litres of water at 95[deg]C were added, and the drum speed was increased to 31 r.p.m. for the washing period. With a drum radius of 80 centimetres this corresponds to a speed at which a centrifugal acceleration of 0.8 g occurs at the drum circumference. The washing period lasted for six minutes. Then, the used washing liquid mixture was evacuated, the drum speed was increased slowly to 3.3 g (62 r.p.m.), and thereafter further raised, at maximum acceleration, to a spinning speed of 250 r.p.m. Spinning was carried out at this speed for two minutes. Two rinsing actions of two minutes duration followed, the speed of drum rotation being reduced to 31 r.p.m. for each rinsing action. After each rinsing action the drum was accelerated to spinning speed. 680 litres of water at 95[deg]C were introduced for each rinsing action. A final rinsing action followed using a further 680 litres of water at 95[deg]C, a final spinning then taking place for ten minutes at 228.5 g (520 r.p.m.). The laundry was then discharged, by slightly tilting the machine, within one minute. The times taken for the various stages were: five minutes for loading, eighteen minutes for washing and rinsing, ten minutes for final spindrying, and one minute for unloading, that is to say a total of thirty-four minutes. Some time also elapsed between stages, namely the times during which the liquid was introduced or exhausted, or the drum was braked after spinning. In total, this time was five minutes and forty seconds. The total duration of the washing programme was, therefore, thirty-nine minutes and forty seconds. The laundry had a residual moisture of 45%. A washing machine constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a part-sectional side elevation of the washing machine together with a laundry feed device and a discharge chute; Figure 2 is a diagrammatic view, on a reduced scale, of the drum of the washing machine during washing or rinsing; Figure 3 is a block circuit diagram. Referring to the drawings, Figure 1 shows a washing machine having a casing 11, the lower part of which serves as a tank 12 for water or liquor. A drum 13 is mounted in the casing 11, the circumferential wall of the drum being perforated, and the drum being rotatable about a generally horizontal axis 41. The axis 41 lies slightly above the centre line of the casing 11, so that a relatively small, narrowing gap is formed between the top of the drum 13 and the casing. A frustoconical hollow shaft 14 extends axially from the drum 13, the hollow shaft having its minimum diameter at the exterior of the machine. The drum 13 is mounted on bearings 15 seated between the hollow shaft 14 and the casing 11. The hollow shaft 14, and hence the drum 13, is driven by a drive motor 18 via a pulley belt 16 and a drive belt 17.The motor 18 is firmly attached to the casing 11 of the washing machine by means of a bracket 19. The entire washing machine is slightly pivotable about a pivot point 20. The pivotal movement is caused by a drive 21, which can be for example hydraulic, pneumatic or electric. Washing liquor is fed to the tank 12 through a flexible conduit 22. The height of the washing liquor in the drum 13 is regulated precisely to a predetermined ideal level 26 by a magnetic valve 23 which is controlled by a bath level sensor 24. Rinsing water is introduced into the tank 12 in a similar manner through the conduit 22 or through a further conduit (not shown), and through indication and regulation means (not shown). As soon as they are no longer required, rinsing water and washing liquor flow away through a discharge valve 25. Laundry articles 28 are conveyed fully automatically in the drum 13 by means of transport apparatus 29 and a chute 27. The hollow shaft 14 is provided with a lid 30 at its free end (charging opening) 40, and the drum 13 is provided with a lid 32 at its free end (discharge opening) 31 the lids serving to close the axial ends of the drum and shaft.During the charging of the laundry articles 28, the lid 30 is open and the lid 32 is closed. The washing machine has a programme control system 34 (see Figure 3) having a device 35 for varying the rotational speed of the drum 13, the device 35 being connected to a tachometer 48 associated with the motor 18. A vibration sensor 47 is connected to a comparator circuit 49, which is connected to the programme control system 34, the tachometer 48 and the motor 18. The device 35 for varying the rotational speed of the drum 13 is switched on during the transition from washing speed to spin-drying speed, and switched off again only after a rotational speed of at least 2 g is reached. The device 35 could be such as to increase the rotational speed in this range purely in dependence upon time. However, in view of the high rotational speeds which are proposed the above-described circuit arrangement is preferable. The washing machine is also provided with heater pipes 42. After the-laundry 28 has been charged into the washing machine, the rotational speed of the drum 13 is slowly increased. This ensures uniform distribution and application of the laundry on the drum 13, and that a centrifugal acceleration having a value of about 1.5 g is generated at the periphery of the drum 13. The loading chute 27 is removed from the charging opening 40 with the aid of a drive 43 which pivots the chute about a hinge 44, and the lid 30 is then closed. the rotational speed of the drum 13 can be lowered to the washing speed and the washing process commences. When the laundry has been washed, the washing machine is tilted slightly about the pivot point 20, so that the discharge opening 31 is lowered a little, and the lid 32 is then opened. With the drum 13 running at moderate speed, this results in the laundry articles 28 flying out of the discharge opening 31, and falling on to a discharge chute 45 which leads to a conveyor 33. The individual loading and unloading programmes for the laundry, and the actual washing, rinsing and spin-drying programmes, are controlled by the programme-control system 34. This programme-control system 34 regulates, in a manner known per se the length of time of the individual operations, the rotational speed of the drum 13, the liquid mixture level, and the liquid temperature. All operations, such as loading, washing, rinsing, spin-drying and unloading, require precisely determined rotational speeds of the drum 13. The rotational speed of the drum 13 is also dependent upon its diameter, which is selected so that the following values for the centrifugal acceleration generated at the periphery of the drum 13 are:- (1) for loading - between 0.3 and 0.5 g, (2) for application of the laundry to the drum wall-from 1.5 g and above, (3) for washing and rinsing - between 0.8 and 0.95 g, (4) for spin-drying - greater than 100 g, and (5) for unloading 0.6 to 0.9 g. It is also possible for the device 35 to be coupled to the vibration sensor 47 so that, as the amplitude of the vibrations decreases, the angular acceleration of the drum 13 increases proportionally, up to a maximum value. In the washing machine shown in Figure 1, the varying load on the motor 18 can be used to control the device 35. As long as the laundry is not evenly distributed in the drum 13, the motor 18 consumes more energy than when the laundry is evenly distributed. This higher energy consumption can be used, for example as a voltage drop across a series resistor 36 in the supply lead to the motor 18, for control purposes. Thus, the lower the voltage drop is, the more rapidly does the device 35 increase the angular acceleration of the drum 13. The connection between the device 35 and the vibration sensor 47 ensures that the angular acceleration is regulated, in the critical range immediately below 1 g, in inverse proportion to the imbalance which is caused by unevenly distributed laundry. Moreover, an imbalancecausing inhomogeneous laundry distribution can result in laundry being detached from the drum wall and deposited elsewhere. This results in running of the drum 13 without imbalance. Figure 2 shows the flight path of laundry articles 28 during the washing and rinsing operations. The rotational speed of the drum 13 is just great enough so that the laundry articles 28 are entrained on the inside of the drum 13, which rotates in the direction of the arrow 37. The rotational speed of the drum 13 generates a centrifugal acceleration which is slightly less than that of gravity.Consequently, the laundry articles 28 detach themselves from the drum 13 before they reach "top dead centre" (at the level of the laundry article 28') and drop in a free flight path, indicated by the arrow 38, to a position 39 on the drum 13 where the washing and rinsing actions occur. The drum 13 dips only into the upper layers of the washing liquor and rinsing liquid. These upper layers are largely free from dirt, because the washing liquor or rinsing liquid is centrifugally accelerated by the rotation of the drum 13, and so the dirt settles, as a result of the centrifugal effect, and collects on the bottom of the tank 12, whence it is removed. Further acceleration of the drum 13 is prevented, when imbalance causes excess vibration, by the device 35 which receives a control signal from the vibration sensor 47, which has a contact which is broken by excess vibration of the machine. Following the resulting deceleration of the drum 13, the programme control system 34 returns to its starting point, and, after a time delay, the programme control system 34 permits acceleration to re-start. This is effected electrically by appropriate actuation of a phase control system (not shown), which increases the energy supply to the motor 18 in proportion to the elapsed time. The washing machine shown in Figure 1 is formed as a cantilever-mounted machine having a through-flow drum. This has the advantage that, for example, hospital laundry and especially infected laundry, can be introduced into one side of the machine and withdrawn from the other. Thus, the machine can be installed against an opening in a partition or wall, and the opening can then be sealed off by resilient sealing means. In this way, the carrying of bacteria to said other side can be prevented. Because of the high speeds of drum rotation, the bearing 15 for the hollow shaft 14 must be chosen carefully. Here, a hydrostatic bearing is advisable, in order to reduce the friction and avoid hot-running. Such hydrostatic bearings are known, for example, for the mounting of highspeed turbines. As already mentioned, the axis 46 of the casing 11 1 lies below the drum axis 41. This eccentric mounting results in braking of the drum 13 after each spinning operation. This is achieved by introducing water into the casing 11 so that the entire washing machine is used as a water-eddy brake. The turbulent water is entrained between the drum 13 and the casing 11. This entrained water builds up, generating a considerable pressure, in the upper region of the machine, the washing being forced away from the drum wall at the same time.

Claims

1. A method of washing laundry in a washing machine having a generally cylindrical, perforated drum rotatably mounted about a substantially horizontal axis in a casing, the method comprising the steps of introducing washing liquor into the casing until the washing liquor just covers the bottom of the inner cylindrical surface of the drum, introducing articles of dry laundry singly into the drum, rotating the drum at a speed which generates a centrifugal acceleration of between 0.3 g and 0.8 g at the drum circumference thereby uniformly wetting the laundry, increasing the drum speed so as to generate a centrifugal acceleration of slightly less than 1 g at the drum circumference, and maintaining this drum speed for a predetermined time in order to wash the laundry.

2. A method as claimed in claim 1, further comprising the step of increasing the speed of rotation of the drum to a spin-drying speed, the transition to spin-drying speed being effected gradually.

3. A method as claimed in claim 2, further comprising the step of reducing the speed of rotation of the drum from the spin-drying speed to that at which the laundry was introduced into the drum.

4. A method as claimed in claim 3, further comprising the steps of rinsing and spinning the laundry at least once after said speed reduction of the drum, the or each rinsing action comprising the steps of introducing water into the casing and increasing the rotation of the drum to a speed which generates a centrifugal acceleration of slightly less than 1 g at the drum circumference, a spinning action following the or each rinsing action, the or each spinning action being effected by gradually increasing the speed of rotation of the drum to a spin-drying speed.

5. A method as claimed in any one of claims 1 to 4, wherein the wetting of the laundry is effected using a quantity of washing liquor sufficient only to give the laundry a pasty consistency.

6. A method as claimed in claim 5, wherein said quantity of washing liquor corresponds to about 30-70% of the absorption capacity of the laundry.

7. A method as claimed in any one of claims 1 to 6, wherein the quantity of washing liquor is such that the height of the level of washing liquor in the drum is less than 5% of the drum diameter.

8. A method as claimed in any one of claims 1 to 7, further comprising the step of introducing a liquid into the casing after the laundry has been uniformly wetted and before the drum speed is increased to the washing speed.

9. A method as claimed in claim 8 when appendant to claim 7, wherein the quantity of liquid introduced is such that the height of the level of liquid mixture in the drum is substantially 10% of the drum diameter.

10. A method as claimed in claim 8 or claim 9, wherein said liquid is water.

11. A method as claimed in any one of claims 1 to 10, wherein the washing liquid is a concentrated washing liquor.

12. A method as claimed in claim 11, wherein the washing liquor is a saturated washing liquor which may have a solid phase present.

13. A method as claimed in any one of claims 1 to 12, wherein, after the uniform wetting of the laundry, washing is effected at a drum speed which generates a centrifugal acceleration of substantially 0.8 to 0.95 g at the drum circumference.

14. A method as claimed in any one of claims 2 to 13, wherein the increase of the drum speed in the range between the washing speed and about 2 g is controlled in dependence upon any balance of the laundry within the drum.

15. A method as claimed in claim 14, wherein, upon imbalance occurring, the drum speed is reduced to less than 1 g, after which the drum is re-accelerated.

16. A method as claimed in any one of claims 2 to 15, wherein spin-drying is effected with a drum speed which generates a centrifugal acceleration of between 3 and 350 g at the drum circumference.

17. A method as claimed in any one of claims 4 to 16, wherein the rinsing water is introduced between the casing and the drum in such a quantity that a considerable back pressure is generated.

18. A method as claimed in any one of claims 4 to 17, wherein there is one washing action and one two or three rinsing actions.

19. A method as claimed in any one of claims 4 to 18, wherein the temperature of the rinsing water does not exceed, and differs little from, the temperature of the washing liquor.

20. A method as claimed in any one of claims 1 to 19, wherein the washing liquor contains detergents.

21. A method as claimed in any one of claims 4 to 20, wherein detergents are added to the rinsing water.

22. A method of washing laundry in a washing machine having a generally cylindrical, perforated drum rotatably mounted about a substantially horizontal axis in a casing, the washing machine being such that, during washing and rinsing actions, laundry in the drum is repeatedly lifted and then allowed to fall on to the lower part of the drum, such that, upon gradual increase of the drum speed the laundry is distributed over the drum wall substantially evenly, and such that, upon further increase of drum speed, the laundry is centrifuged, the method comprising the steps of introducing articles of dry laundry singly into the drum, introducing washing liquor into the casing until the washing liquor just covers the bottom of the inner cylindrical surface of the drum, rotating the drum at a speed which generates a centrifugal acceleration of between 0.3 and 0.8 g at the drum circumference thereby uniformly wetting the laundry, increasing the drum speed so as to generate a centrifugal acceleration of slightly less than 1 g at the drum circumference, and maintaining this drum speed for a predetermined time in order to wash the laundry.

23. A method of washing laundry substantially as hereinbefore described with reference to the accompanying drawings.

24. A method of washing laundry substantially in accordance with the example described above.

25. A washing machine having a generally cylindrical, perforated drum rotatably mounted about a substantially horizontal axis in a casing, a liquid level sensor for sensing the level of liquid in the drum, a programme control system, and a device for controlling the rotational speed of the drum, said device comprising a vibration sensor which is connected to the programme control system and the motor through a comparator circuit and wherein the motor is provided with a tachometer which is attached to the comparator circuit.

26. A washing machine as claimed in claim 25, wherein the drum has a loading opening at one end and a discharge opening at the other end, said openings being concentric with the drum axis.

27. A washing machine as claimed in claim 26, wherein the diameter of the discharge opening is larger than 120 mm.

28. A washing machine as claimed in claim 26 or claim 27, wherein the drum is pivotably mounted within the casing.

29. A washing machine as claimed in claim 26, wherein the loading opening is formed as a hollow frustoconical shaft whose wider end is rigidly attached to the drum.

30. A washing machine as claimed in claim 29, wherein the drum is mounted in the casing by means of the hollow shaft.

31. A washing machine as claimed in claim 30, wherein the hollow shaft is supported in the casing by means of a hydrostatic bearing.

32. A washing machine as claimed in any one of claims 26 to 31, wherein a chute is provided for directing laundry into the loading opening.

33. A washing machine as claimed in claim 32, wherein means are provided for pivoting the chute away from the loading opening.

34. A washing machine as claimed in any one of claims 25 to 33, wherein a gap is situated between the drum and the casing, the gap being a tapered cross-section.

35. A washing machine as claimed in claim 34, wherein the tapering gap results from an eccentric arrangement of the drum in the casing.

36. A washing machine as claimed in any one of claims 25 to 35, wherein the drum has no carrier fins.

37. A washing machine as claimed in any one of claims 25 to 36, wherein the drum has a diameter of between 800 and 2000 millimetres.

38. A washing machine substantially as hereinbefore described with reference to, and as illustrated by the accompanying drawings.