US3263741A - Automatic temperature control system for extruding machines - Google Patents

Description

Aug. 2, 1966 J. G. E. WILLIAMS 3,263,743

AUTOMATIC TEMPERATURE CONTROL SYSTEM FOR EXTRUDING NCHINS Filed May 20, 1964 2 Sheetshee, l,

AUTOMATIC TEMPERATURE CONTROL SYSTEM Foa EXTRUDINC MACHINES Filed ay 20, 1964 Aug. 2, 1966 J. ca. E. wiLLlAMs 2 Sheets-Sheet 2 United States Patent() 3,263,741 AUTOMATIC TEMPERATURE CONTROL SYSTEM FOR EXTRUDING MACHINES John G. E. Williams, Islington, Ontario, Canada John Williams Machinery Ltd., Cooksville, Ontario, Canada) Filed May 20, 1964, Ser. No. 368,798 4 Claims. (Cl. 165-39) This invention relates to a new and improved temperature control system especi-ally adapted to extruding machinery for accurate temperature control of polymer melt which has lalways been a difficult problem in extruding plastic and similar materials. Higher screw feeds and higher outputs have demanded increasingly improved ternperature control systems for the extruder. Ever increasing polymer viscosity makes it imperative that a highly efficient system of melt temperature control be provided, and this is the primary object of the present invention.

The present invention achieves this object by providing a series of jackets about the barrel of the extruder, said jackets being connected with a substantially enclosed heat exchanging liuid pump system wherein the coolant is pumped separately into each end of each jacket, and traverses the jackets, about the barrel, in opposite directions in completely separate streams, being let out at the opposite ends of the barrel jackets. These Itwo separate streams of liuid never come in contact With each other inside of each barrel jacket, and this produces a very flat differential curve across each barrel section as opposed to the conventional large temperature differential where all the fluid may be fed into one end of the jacket and out the other. In -other words, the present invention provides an extremely even cooling of the entire barrel from endto-end thereof, or in certain selected areas thereof.

Furthermore the present invention also contemplates the use of a thermal switch operating a solenoid on-and-off valve at the output side of each of the barrel jackets, together with controls for a pump for the input, so that when cooling is called for in any one of the jackets, the valve will open and the pump `will operate, it thus being seen that there is always liuid in each jacket at all times and that system is very eliicient. Furthermore, means is provided for adjusting the temperature of the cooling fluid so that it is variable for different rates of heat removal necessary for different extrusion conditions.

There are only four methods of controlling melt temperature. These include a different screw design for every polymer to enable performance under all speed ranges and input horespowers, holding the extrudate melt temperatures within the minimum and maximum polymer melt range, but this is impossible to do and even if possible would be too expensive.

The second method is by air cooling but this depends upon the ambient temperature which can vary from sixtytive degrees to as high as one hundred and ten Fahrenheit. Refrigerated air is not generally used because of the high condensation rate.

The third system is water cooling, but although water has a high B.t.u. per hour removal rate, it also has a high thermal shock characteristic, and since water boils at 212, modern systems have to operate under extremely high pressures. With a-ir cooled Vapor condensers there is the same problem as with conventional air cooling as the differential plant temperatures range from 65 F. to 110 F., reducing the efficiency of the cooling system. In the present case it is preferred that a heat transfer liuid be used which has approximately one-half Iof the specic heat of water, thus providing for a low internal pressure and a high boiling point.

Other objects land advantages of the invention will appear hereinafter.

31,263,741 Patented August 2, IQG

Reference is to be had to the accompanying drawings in which:

FIG. 1 is a diagrammatic view which illustrates the invention;

FIG. 2 is a view in side elevation illustrating the jacket mechanism, parts being broken away;

FIG. 3 is a section on line 3-3 of FIG. 2, and

FIG. 4 is a longitudinal section through a jacket.

Referring now to FIG. 1, there is here shown the extruder barrel 10 and by way of illustration there are indicated to be four barrel cooling jackets, each one of -which is substantially the same as each of the others, and these are indicated generally by the reference numeral 12. They are applied directly to the barrel. Also there can be more or less of these jackets, depending upon the situation encountered. The jackets 12 are substantially surrounded by electric heating appliances las indicated in FIG. 4. These appliances are normally wrapped around and clamped down tightly on the jackets and may be of several different commercial types.

Each barrel cooling jacket 12 is provided with two entrance points for the coolant, these entrance points being at the opposite ends of each jacket as at 14 and 16 as to the barrel jacket indicated at the extreme left in FIG. 1 and at 18 and 20 in the others. The coolant spirals co-mpletely about the barrel from each end thereof to the opposite end, exiting at 22 and 24 as tothe barrel jacket lat the extreme left and at 26 and 28 in the other jackets. The dotted lines at 30 indicate in general the course of the coolant from the entrance 16 to the exit 22 and from entrance 14 to exit 24; whereas the dotted lines at 32 indicate the course of the coolant from the entrances 18 and 20 and to the exits 26 and 28, it being understood however that these are representative only and will be described more fully hereinafter as lying in spiral paths about the barrel and completely separate one from the other.

It -is to be noted that in FIGS. 2 and 3 the piping, etc., has been largely omitted as it is relatively conventional and well within the knowledge of those skilled in'the Iart, and it is believed that the entire invention can be understood from `an inspection of the figures presented herein.

The coolant is pumped in through lines 34 from a pump 36 connected with respect to a check valve and strainer tank 38 and preferably derived from a heat exchanger 40 of well-known design. As indicated, various gauges, drain, cooling water inlet, etc., as will be clear to those skilled in the art are used with this system .as well as the relief valve which is indicated at 42 and the return line at 44.

The various exits 22, 24, 26 and 28 are connected in pairs through strainers to thermally operated solenoid offend-on valves which are indicated at 46. These are all independently operated and controlled -by conventional means including probes, one for each cooling jacket, which extend as close to the interior of each barrel as is possible in order to provide for accurate control.

It is pointed out that when the probe calls for cooling, wherever it may be set, it is connected with respect to a thermal control system of well-known and. conventional design `for the purpose of opening whatever valve or valves 46 may be called for, depending upon the zone where the cooling is indicated, and at the same time turning on the pump 36. Immediately the coolant starts to flow through the jackets from each end thereof to the opposite end, through the valves, and back to the outlet header at 48 which leads as shown in FIG. 1 back to the heat exchanger 40. When the probe ysignals that a proper temperature is reached, the valves 46 or any of them, are shut ofi, and the pump will also shut olf but only when all valves close.

Now referring to FIGS. 2, 3 and 4, the extruding screw is clearly represented at 50 and is surrounded by the liner 51 and barrel 10. The barrel 10 is encompassed by a series of cooling jackets 12 which are in intimate contact with the outside of barrel 10. At its periphery each jacket is provided with two separate spiral grooves 54 and 56, these being closed off by member 52 or any other way. The jackets 12 are completely independent of each other so that there is no interference. As shown in FIG. 3, the entrances and exits are respectively located 180 from each other and this means that as the coolant enters 'as for instance at 16 in FIG. 1, it spirals about the -cooling jacket of the barrel exiting at 22, and Where it enters at 14 it runs in the reverse direction exiting at 24. The construction of the other jackets are the same except that the entrance and exit points have been shifted as to the points 14 and 22 to a 180 situation in order to more easily accommodate the piping. A probe is indicated at 58 and is connected to a conventional tem- -perature control device 60, in turn connected to operate the valves and the pump.

It is believed that the objects of the invention have been satisfied by the construction above recited and that the advantages of the invention Will be clearly recognized. To illustrate the tremendous cooling capacity of this novel system, a three-and-a-half inch extruder running on rigid PVC Was stopped, heating turned olf, full cooling applied, with the melt temperature being dropped to 200 F. in seven minutes, the calculated heat removal rate was found to be `a phenomenal 270,000 B.t.u. per hour. While the machine Was running, manual cooling was applied to the front zone closest to the die, and the cooling held on for seven seconds. A deep tted thermal couple probe, installed Very close to the barrel liner, recorded a sixty degree Fahrenheit temperature drop. This temperature control system produced 4a temperature drop of 8.75 F. per second. With the front three zones of a six-inch diameter extruder equipped with the present invention and the three rear zones equipped with conventional air cooling, the machine was stopped, with full cooling according to the present invention applied on the front zones aud full air cooling applied to the three rear zones. The zones tted With the invention described herein dropped in temperature from a 450 F. to 200 F. in sixteen minutes, while the three air-cooled zones dropped from 450 F. to only 400 F. at the same time.

Having thus described my invention and the advantages thereof, I do not Wish to be limited to the details herein disclosed, otherwise than as set forth in the claims, but what I claim is:

1. The combination with an extruding machine which includes a barrel, extruding mechanism therein, and heater elements on the barrel, of a cooling construction therefor wherein the cooling construction comprises a source of fluid coolant, a jacket about the b-arrel, means for introducing the coolant at each end lof the jacket, means in the jacket providing passages leading the coolant about the barrel to the opposite ends thereof, and exit outlets at said opposite ends for the coolant after it has traversed the jacket relatively longitudinally with respect to said barrel from end-to-end of said jacket in opposite directions, and means operatively connected with respect to said source to force the coolant through the jacket passages.

2. The combination recited in claim 1 wherein said passages are arranged spirally in the jacket, said spiral passages running about the barrel.

3. The combination recited in claim 1 including valves located at the outlets for the coolant, and thermostatic controls and sensors therefor, the controls operating the valves and the pump simultaneously.

4. The combination recited in claim 1 including valves located at the outlets `for the coolant, and thermostatic controls and sensors therefor, the controls operating the valves and the pump simultaneously, a heat exchanger receiving the coolant after it has passed through the jackets and said valves, the heat exchanger supplying the coolant to the pump.

References Cited by the Examiner UNITED STATES PATENTS 1,951,427 3/ 1934 Lodge. 2,688,770 9/1954 Henning 18-12 2,721,729 10/1955 van Riper 16s- 64 FOREIGN PATENTS 869,890 5/ 1961 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

N. R. WILSON, Assistant Examiner.

Claims (1)

1. THE COMBINATION WITH AN EXTRUDING MACHINE WHICH INCLUDES A BARREL, EXTRUDING MECHANISM THEREIN, AND HEATER ELEMENTS ON THE BARREL, OF A COOLING CONSTRUCTION THEREFOR WHEREIN THE COOLING CONSTRUCTION COMPRISES A SOURCE OF FLUID COOLANT, A JACKET ABOUT THE BARREL, MEANS FOR INTRODUCING THE COOLANT AT EACH END OF THE JACKET, MEANS IN THE JACKET PROVIDING PASSAGES LEADING THE COOLANT ABOUT THE BARREL TO THE OPPOSITE ENDS THEREOF, AND EXIT OUTLETS AT SAID OPPOSITE ENDS FOR THE COOLANT AFTER IT HAS TRAVERSED THE JACKET RELATIVELY LONGITUDINALLY WITH RESPECT TO SAID BARREL FROM END-TO-END OF SAID JACKET IN OPPOSITE

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