GB2160225A

GB2160225A - Solvent cleaning apparatus

Info

Publication number: GB2160225A
Application number: GB08414958A
Authority: GB
Inventors: Gordon E Littleford; John B Stevens
Original assignee: TERMO TECHNIC Ltd
Current assignee: TERMO TECHNIC Ltd
Priority date: 1984-06-12
Filing date: 1984-06-12
Publication date: 1985-12-18
Also published as: GB2160225B; GB8414958D0

Abstract

Solvent cleaning apparatus comprises a tank (10) for solvent (12) having cooling coils (18) above to condense any vapour from the solvent. The cooling coils (18) form a part of a refrigeration system (20) including a compressor (22), condenser (28), restrictor (30), evaporator (18) and an auxiliary evaporator (38) adapted to add heat to the system to allow more accurate control of the compressor temperature. Variable speed fans (32,40) are controlled by electronic means (34,44) responsive to temperature sensors (36,42) to control the amount of heat dissipated by, and hence temperature of, condenser (28) and heat absorbed by, and hence temperature of, evaporator (38) respectively. <IMAGE>

Description

SPECIFICATION Solvent cleaning apparatus This invention relates to solvent vapour cleaning apparatus and particularly to low temperature liquid solvent cleaning apparatus. Solvent cleaning apparatus may comprise a tank of solvent including means to heat and boil the solvent and means to vibrate ultrasonically the solvent. It is usual also to include cooling means around the top of the tank to condense vapour given off by the solvent to retain it in the tank. Such cooling means may form part of a refrigeration system since the optimum temperature therefor is usually about 5 C that is, the temperature is just above the freezing point of water so as to avoid frosting of the coils but well below the boiling point of the solvent so as to condense the solvent vapour as efficiently as possible.

Some apparatus dispense with the ultrasonic vibrating means and rely entirely on the boiling solvent and/or vapour to undertake the cleaning action required. However, where the articles to be cleaned are particularly temperature sensitive, such as some electronic components for instance, then it is desirable to dispense with the heating means and rely solely on the innate cleaning action of the cold solvent-perhaps supplemented with ultrasonic vibration. In some cases the solvent is heated to some specific sub-boiling temperature to increase cleaning efficiency without damaging the components being cleaned.

Again this may be accompanied by ultrasonic vibration.

While it is found that loss of solvent through vapour dissipation is not such a significant problem where the solvent is relatively cool, or at least not boiling, it nevertheless still occurs that when articles are withdrawn from the tank, vapour can be dragged out.

Sometimes the heater thermostat may be faulty and boil the solvent or the work load might be hot or even there may be high ambient temperature, any of which may lead to solvent vapour being driven off. For any of these reasons therefore it is still found to be worthwhile to include cooling means in such cold solvent cleaning apparatus to retain solvent vapour in the tank.

However, it is proving difficult to control the temperature of the cooling coils and it is an object of this invention to provide apparatus having better control over cooling coil temperature.

In accordance with this invention there is provided solvent cleaning apparatus comprising a tank or container for solvent and cooling means disposed in the tank above the intended level of solvent in the tank to condense any vapour given off by the solvent, said cooling means forming an evaporator of a refrigeration system further comprising a compressor to compress refrigerant vapour, a condenser to condense the refrigerant and dissipate heat, a restrictor to reduce the pressure of the refrigerant, the evaporator in which the refrigent vapourises and cools absorbing its heat of vapourisation and an auxiliary evaporator for the further absorbtion of heat from ambient surroundings.

By thus placing an artificial load on the refrigerant-that is by warming it up other than through condensing solvent vapour in the container-it is much simpler to control the temperature of the evaporator.

Preferably agitation means is provided to promote heat exchange between the condenser and its surroundings. Where said means is a fan, preferably it is a variable speed fan whose speed is controlled by control means arranged to increase the speed of the fan in response to an increase in temperature of the refrigerant at the output of the condenser.

Preferably similar means are provided for the auxiliary evaporator except that here the control means is arranged to decrease the speed of the fan in response to an increase in the temperature of the input to the auxiliary evaporator.

Thus minor changes to the load on the primary evaporator are easily compensated by the auxiliary evaporator control means and the temperature of the former is simply maintained at the desired level.

The invention is further described hereinafter with reference to the accompanying drawing in which solvent cleaning apparatus in accordance with the invention is schematically illustrated.

In the drawing a tank or container 10 is filled to a desired level with solvent 12 such as a fluorinated or chlorinated hydrocarbon.

Articles to be cleaned are inserted into the container of solvent. Ultrasonic vibrating means 14 may be provided to assist soil removal. Where this is the case heating means, for instance a limpet heater 15, may also be provided to heat the solvent 12 to some sub-boiling temperature to enhance the ultrasonic cleaning action. A temperature sensor 17 is provided to control the heater 15.

Adjacent the open top 16 of the tank 10 cooling coils 18 are disposed. The cooling coils form a primary evaporator 18 of a closed refrigeration system 20 described further hereinbelow. The cooling coils are provided to condense any solvent vapour coming into contact there with which may have been driven off the liquid solvent 12 through, for instance faulty operation of sensor 17 or through the introduction of a hot workload, etc.

The refrigeration system 20 comprises pipework 21 interconnecting a compressor 22, via a high pressure switch 24 and strainer 26, with a condenser 28. A restrictor 30 maintains a high pressure of refrigerant in the condenser 28. The refrigerant in the conden ser therefore condenses giving up its heat of vapourisation which is dispelled to the ambient atmosphere by means of a variable speed from 32. The speed of the fan 32 is controlled by electronic control means 34 which is responsive to the temperature of the condenser 28 and monitored by sensor 36. The electronic control means 34 operates in such a way that, as the temperature detected by sensor 36 increases, so the speed of the fan 32 is increased.

The temperature of the refrigerant adjacent sensor 36 is therefore accurately maintained at a level determined by the electronic control means 36.

As the refrigerant passes through the restrictor 30 it expands and is reduced in pressure. In the evaporator 18 the refrigerant evaporates absorbing its heat of vapourisation and being reduced in temperature-to a level dependent essentially on the temperature of the refrigerant passing sensor 36.

However, because the solvent 12 in tank 10 is not boiling there is little heat input to the refrigerant in evaporator 18. Consequently the temperature of the refrigerant leaving evaporator 18 and passing to auxiliary evaporator 38 remains low. A variable speed fan 40 blows across the auxiliary evaporator 38 and so since ambient air will normally be at about 20 C and the refrigerant will be at about 50 C the refrigerant will absorb heat.

A sensor 42 detects the temperature of the refrigerant leaving the evaporator 18, and through electronic control means 44 adjusts the speed of the fan 40. The electronic control means 44 operates in such a way that, as the temperature detected by the sensor 42 increased (because of instance solvent vapour condenses on the coils 18) the speed of the fan 40 is decreased. Thus the temperature of the refrigerant leaving the auxiliary evaporator 38 is accurately controlled.

The refrigeration system 20 is such that a nett amount of heat is added to the system by the compressor 22. Since heat losses through the hot side of the system are minimal compared with the heat added it is necessary, if a heat balance is to be achieved, for the fan 34 to be operating at least at a low speed all of the time.

Furthermore in order to reduce fluctuations in the temperature of refrigerant entering the compressor it is necessary to maintain that temperature at a relatively high level and this is achieved by arranging for the fan 40 to operate. It ceases to operate of course should a load be placed on the coils 18 and the temperature of the refrigerant be raised through that cause.

On the other hand should the temperature at the sensor 42 drop because no load is placed on the coils 18 then instead of allowing the temperature of the compressor to drop as well, the speed of the fan 40 is increased thereby adding heat to the system.

Such an arrangement reduces the frequency at which the compressor needs to be switched on and off and provides better control of the temperature of the coils 18.

Solvent which does condense on the coils 18 is collected in a peripheral gutter 19 and is returned to the tank 10 by a coduit 21~possibly via a water separator and/or intercooler (neither being shown).

Claims

1. Solvent cleaning apparatus comprising a tank or container for solvent and cooling means disposed in the tank or container above the intended level of solvent in the tank, said cooling means forming an evaporator of a refrigeration system further comprising a compressor to compress refrigerant vapour, a condenser to condense the refrigerant and dissipate heat, a restrictor to reduce the pressure of the refrigerant, the evaporator in which the refrigent vapourises and cools absorbing its heat of vapourisation and an auxiliary evaporator for the further absorbtion of heat from ambient surroundings.

2. Solvent cleaning apparatus as claimed in claim 1 further comprising condenser agitation means to promote heat exchange between the condenser and its surroundings.

3. Solvent cleaning apparatus as claimed in claim 2 in which said agitation means is a fan blowing or drawing ambient air through said condenser.

4. Solvent cleaning apparatus as claimed in claim 3 further comprising electronic control means which is responsive to the temperature of the refrigerant in the condenser to alter the speed of said fan.

5. Solvent cleaning apparatus as claimed in any preceding claim further comprising auxiliary evaporator agitation means to promote heat exchange between said auxiliary evaporator and its surroundings.

6. Solvent cleaning apparatus as claimed in claim 5 in which said auxiliary evaporator agitation means is another fan blowing or drawing ambient air through said auxiliary evaporator.

7. Solvent cleaning apparatus as claimed in claim 6 further comprising electronic means which is responsive to the temperature of the refrigerant in the evaporator to alter the speed of said other fan.

8. Solvent cleaning apparatus substantially as hereinbefore described with reference to the drawing.