US 2123439 A
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Description (OCR text may contain errors)
y 2, 4 J. AVA E 2,123,439
METXiOD OF DEGREASING Original Filed May 5, 1933 31 \30 INVENTOR.
osepa SAVAGE VATYTORNEX .as trichlorethylene.
Patented July 12,
METHOD OF. DEGREASING Joseph Savage, Weston Point, Bnncorn, England,
assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Original application May 5, 1933, Serial No.
Divided and this application October 7, 1935, Serial No. 43,888. In Great Britain May 6, 1932 1 Claim.
This invention relates to an improved method for degreasing by means of volatile solvents such This application is a division of my copending application S. N. 669,610, filed May 5, 1933 now Patent No. 2,020,335 issued Nov. 12, 1935.
A large number of methods and types of apparatus have been proposed for the removal of grease and fat from various types of material, in which cooling surfaces are employed for the cooling and condensation of the vapours of the volatile solvent,'the condensate being subsequently returned to the apparatus. In some cases the cooling surfaces are used for cooling a body of liquid solvent or a chamber through which materials to be degreased are passed before or during treatment.
Experience has shown that these cooling suri faces have a tendency to condense water from the atmosphere in addition to cooling and condensing the solvent. This condensed water then becomes associated with the solvent and thus comes into contact with the metal parts of the apparatus and with the material being treated. This increases the tendency of the metals to corrode and is .particularly objectionable in the degreasing of metal goods such as iron or steel.
According to the invention .I warm, to apredetermined extent, the cooling waterwhich is used and thereby maintain the cooling and condensing surfaces at a temperature above the dew point of the atmosphere in which the operation is carried out, but substantially below the condensing temperature of the solvent. As a further feature of the invention, the solvent vapours are first brought into contact with the said cooling surfaces and then uncondensed vapours are brought into contact with still cooler surfaces. The condensate from these last surfaces, which may be a mixture of solvent and water, is collected separately from that of the solvent vapour obtained from the first cooling surfaces. Complete condensation is thus effected while at the same time the main bulk of condensate remains uncontaminated by water. In the degreasing of metal goods by means volatile solvents, the process may be carried out in the vapour phase or in the liquid phase, that is the goods may be exposed to the vapour of a volatile solvent or may be washed by a hot or cold liquid solvent. Combinations of these various methods of working may also be made. The present invention is of course only applicable to processes involving vapour phase degreasing or treatment of the goods with heated liquid solvent. In most forms of apparatus for carrying out these processes the cooling surfaces consist of pipes through which a supply of cold water ows. In such cases I maintain the desired temperature of the cooling surface by slightly warming the inlet water before admitting to the cooling pipes. Thismay be done in many ways, for example, by passing the water through a small electrical heater or gas heater, either of which may be conveniently controlled by a thermostatic device. This method is applicable when vapour phase degreasing is used alone or when vapour-phase degreasing follows a treatment with cold liqu'id solvent.
In an alternative method, in processes and apparatus using a degreasing bath of solvent liquor at a raised temperature and with cooling coils arranged above the surface, I pass the cooling water through coils arranged in such a heated bath prior to its passage through said 'cooling coils. In this case the number of coils immersed in the liquid and the velocity of the cooling water are adjusted so that the desired temperature ofthe cooling surfaces is obtained. This method may also be applied when the process is a combination of vapour phase and liquid phase degreasing using the liquid at an elevated temperature.
An apparatus adapted for. carrying out the process, referred to in the preceding paragraph, is illustrated in the accompanying drawing, in which Figure 1 shows an elevation and Figure 2 a plan of the apparatus. Referring to Figure 1, the apparatus comprises an outer casing l inside which are located the degreasing chambers 2 and 3 adapted to hold a body of liquid, and separated by the wall 4. Chamber 2 is used for degreasing in the liquid phase and 3 for degreasing in the vapour phase. Both chambers are open to the vapour space I2 in the upper portion of the easing I. The wall 4 is preferably constructed in the form of a double wall so as to possess an insulating value retarding the transference of heat between the chambers 2 and 3. This enables the temperature of the chamber to be more easily controlled if it is desired to work below the boiling point of the solvent used.
Heating means are provided for each chamber: in the present case. the gas burners 5 and B are used for this purpose although suitably arranged steam coils or electrical heating devices may be used instead. Waste gases from the burners pass to the outlets I, I by way of the space 8 left between the container 1 and the degreasing chambers 2 and 3. This space, in addition to providing a path for the waste gases, also acts as an insulating jacket for the degreasing chambers and thus obviates excessive loss of heat by radiation.
to supply the vapour for the vapour phase degreasing. In. chamber 2 the thermostat may, if
desired, be used to control the temperature at some selected point below the boiling-point oi the solvent.
Cleaning doors in anddrain cocks H are fitted to the base of each degreasing chamber. In the I lower portion of each of the degreasing chambers perforated plates I! are fitted. These plates serve to carry the goods being treated and must be so arranged as to permit the total immersion of the goods in the solvent liquid or vapour, and also in the case of thechamber 3, to prevent contact of the goods with liquidsolvent in the base of the chamber. 1
A set of coils I4 is arranged in the upper portion of the chamber 2.
obstruct the passage into and out of the chamber of goods being treated. A suitable connection i5 to the main2l, and provided with a valve 23 is iarranged for the supply of water to the coils and an outlet pipe ll connecting through the pipes and 25 to the condensing coils I9, is provided. I also find that it is advantageous to fit a shield ll for the protection of the coils ll against damage that might be caused by introducing or withdrawing the goods.
Towards itsupper end the dividing wall 4 is provided with a small overflow outlet i8 leading from the chamber 2 to chamber 3 to enable excess liquid in 2 to pass into 3 at a relatively slow rate. This overflow is placed slightly higher than the cells it but at such a distance from the top of the wall 4 as to avoid a flow of liquid over the top or the wall into chamber 3 when goods are introduced into the normal volume of liquid in chamher 2. I
' In the upper portion of the casing I at any convenient height above the wall 4, condensing coils I! carried by the supports 20 are arranged round the walls. The supply of water to these coils is from the coils H as previously stated and also.
from the main 2| through the pipe 22, fitted with a valve 24. and pipes 25 and 28. At any convenient point after the junction of the pipes l6 and 22 a pocket 21 carrying a thermometer is provided for the observance of the temperature of the water entering the condensing coils. The outlet 28 for the water from the condensing coils leads to waste. Below the condensing coils, around the walls of the casing and adapted to collect the condensate flowing from the coils and the walls of the casing, is arranged a gutter or channel 29. Condensed solvent collected by the gutter is delivered to the two-way cocl: 30 whence it flows by way of pipe ll back to the chamber 2 or by way of 32 to a receptacle not shown, for clean condensed solvent.
A suitable cover (not shown) may be provided for the apparatus to prevent the loss of solvent The coils are placed. I close to the walls of the chamber in order not to mences to flow through the overflow ll. Solvent is also introduced-into the chamber 3, but in this case the volume must be. adjusted sothat it's j surface is below the perforated plate It even when it is in a state of ebullition. It will be obvious that this is a necessary precaution if the efllcient degreasing of goods resting on the plate I: is to be obtained, since after the apparatus has been in use for'some' time the solvent becomes charged with dissolved oils and if allowed to contact with the goods will leave a deposit or film of oil thereon which may not be removed while the goods are being raised through the vapour prior to removal from the apparatus.
After charging the apparatus with solvent the temperature of the chamber 2 is raised to the desired figure by means of the gas burner 5 and the solvent in 3 is heated to boiling to provide for the vapour phase degreasing. At the same time the condensing coils I! are put into operation. The temperature of these coils is adjusted as required by the invention by suitably. proportioning the feed of water through the coils H to the feed coming directly from the main, the valves 23 and 24 being provided for this purpose. It would of course be possible to maintain the water at the .required temperature by passing the whole supalso desirable in order that any solid impurities such as swarf or dust, which may be adhering to the goods, may be removed by the mechanical chamber '8 for removal of the. residual fllm of oily matter which is effected by the' condensation thereon of the solvent. It will,'of course, be obvious that when working in this manner the liquid phasedegreasing must be carried out at a temperature sufliciently below that at which the solvent boils, in order that the goods may condense an appreciable amount of solvent when'exposed to the vapour.
" Reference has previously been made to the desired temperature in the liquid phase degreasing chamber2. When working with trichlorethylene washing action of the liquid. After this exposure 1 of the liquid, the goodsare transferred to the I have found this to be about 20-30 0. below in a solvent vapor bath and limiting the upward,
extent of said solvent vapor bath by condensing the residual vapours by bringing them first into contact with cooling surfaces maintained at a temperature above the dew point of the atmos- .phere in which the operation is carried out, but
substantially below the condensing temperature of the solvent, and then into contact with still cooler surfaces, the condensate from these last surfaces, which may be a mixture of solvent and water, being collected separately from that of the solvent vapours obtained from the first cooling surfaces.