Patent GB-616341-A (GB)
Title: Improvements in the manufacture of lubricating grease
Filed: 1945-03-26
Abstract: <PICT:0616341/III/1> <PICT:0616341/III/2> <PICT:0616341/III/3> In a continuous process for the manufacture of lubricating grease from oil and a stiffening agent, such as a soap, the oil and agent are first mixed and then caused to flow in the desired relative proportions in a continuous stream and in a relatively thin confined layer through a zone having a heat-transfer wall.  The thin layer of mixture is heated in the zone through the heat-transfer wall, to a temperature at least sufficient to effect solution of the stiffening agent in the oil, films of the mixture are continuously and rapidly removed from the heat-transfer wall and vigorously and continuously mixed with the remainder of the mixture in the zone by mechanical means.  The mixture is thereby heated extremely rapidly in the thin confined layer to a uniform temperature and a thorough and intimate distribution of the stiffening agent in the oil is effected to produce a grease of uniform consistency.  The word "thin" in the expression "thin confined layer" is to be interpreted as relative to the diameter of the heat - transfer chamber. Ordinarily, the thickness dimension of the layer to be agitated should not be substantially more than about 10 per cent of the dimension of the inner diameter of the heat-transfer chamber.  The mixture may be caused to flow through the zone under pressure and the zone may be elongated and annular.  The mixture may be de-aerated before its passage through the zone and the oil and stiffening agent may be pre-mixed at a temperature substantially below that at which the agent is soluble in the oil, e.g. at room temperature.  Moisture may be flashed off from the mixture, e.g. under vacuum, after its passage through a heating zone.  After emerging from the heating zone the solution may be passed in a relatively thin confined layer through an elongated cooling zone functioning in the same manner as the heating zone, the grease being cooled in the cooling zone to a temperature substantially below that at which the stiffening agent is soluble in the oil. After its passage through the cooling zone, the cooled grease may be passed through a confined space of relatively large cross-section whilst maintaining the temperature of the grease in said confined space substantially equal to that at which the grease is discharged from the cooling stage, thereby providing a time lag during which gelation of the grease can take place.  The gelled grease may then be discharged continuously from the confined space and further cooled while it is simultaneously worked mechanically in a fourth zone.  The soap stiffening agent which is pre-mixed with the oil may be prepared by mixing continuously a fat and a saponifying agent in predetermined relative proportions and causing the mixture to flow continuously and rapidly and in a relatively thin confined layer under pressure through a heating zone of the type previously described.  In this zone the mixture is raised to a temperature sufficiently high to cause saponification and films of mixture are continuously removed from the heat-transfer wall and vigorously mixed with the remainder of the mixture in the confined layer.  The soap stiffening agent thus formed is then continuously pre-mixed with the oil and may be de-aerated and moisture may be flashed off therefrom under vacuum before the pre-mixing operation.  In an example of the process shown in Fig. 1, a premanufactured soap and a mineral lubricating oil are pre-mixed at room temperature in tank 10 to form a slurry of soap dispersed in oil.  In the case of light-bodied greases, the slurry is delivered via control valves 14 and 15, discharge lines 13 and 16 and pump 17 to the heating unit 18.  When a heavy-bodied grease is being made, the oil-soap slurry may require de-aeration by passage into the deaerating chamber 21 via line 19 and valve 20, valve 15 being closed.  The de-aerated slurry then passes to the pump 17 via valve 23 and line 22.  The heating unit 18 (Figs. 1, 3 and 4) includes a chamber 26, Figs. 3 and 4, having the form of an annular, confined space about 3/4 inch thick between the peripheral wall 27 of cylindrical vessel and a comparatively large core 28 mounted therein so as to be capable of rotation.  The core is provided with scrapers 29 which engage the wall 27, constituting an agitator which may be driven at relatively high speed via the shaft extension 30. Surrounding and spaced from the wall 27 is a jacket 31 providing an annular space for the heating fluid (e.g. steam or "Dowtherm") which may enter through a valve-controlled inlet 32 at one end and be discharged through an outlet 33 at the other end.  The pump 17 delivers the slurry to an inlet 34 at one end of the heating unit, and the heated and mixed material is discharged through an outlet 35 at the opposite end.  The heating jacket is encircled by a layer of insulation 36.  The oil soap slurry is forced continuously through the heater 18 under a pressure sufficiently high to prevent vaporization of the oil or of any moisture that may be present.  The combination of temperature increase and vigorous agitation in the heater causes the soap to dissolve in the oil and the solution is passed from the outlet 35 to a cooling unit 38, Fig. 1, which may be similar in construction and operation to the heating unit 18.  Where the soap used for the manufacture of the grease contains an undesirable amount of moisture, this may be wholly or partially eliminated from the soap solution by closing valve 39 and opening a valve 41 in a line 42 leading to a closed flash tank 43.  The pressure in the flash tank may be maintained at any desired figure below that in the heater by suitable adjustment of the three-way valve 48 and the moisture content of the soap in oil solution leaving the dehydrator via the delivery line 44 thereby controlled.  The hot grease is then pumped by the pump 46 into the inlet of the cooling unit 38, the jacket of which communicates with a source of a cooling liquid such as refrigerated brine or cold water through pipes 51 and 52. In most cases the grease issuing from the cooling unit will be sufficiently stable and free from syneresis to permit of its being delivered via lines 53 and 54 and valve 55 to the packaging apparatus.  Alternatively, when desirable, the grease may be passed via line 53 and valve 56 to the working unit 57 in which the grease is relatively slowly worked, e.g. by means of an agitator rotating at 100 to 300 r.p.m., while being cooled to about 90 DEG  to 150 DEG F. and passing in relatively large volume through a chamber maintained under controlled pressure, before being delivered to the packaging apparatus via line 58 and line 59. With some greases, more particularly lithium base greases from light viscosity oils and some aluminium base greases, it has been discovered that improved gel structure is obtained by providing a time lag or gelling time before the final working and cooling step.  Thus, in the case of lithium base grease, the cooler 38 may rapidly cool the grease down to about 210 DEG  F. while the agitator is rotating at 300 to 700 r.p.m. and the grease may be passed via pipe 99 to the elongated chamber 98 through which it flows without agitation in from 10 to 30 minutes. The grease may then discharge through pipe 100 to the working unit 57 at about 185 DEG  F.