US 2640788 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
June 2, 1953 J.- F. ROCKETT, JR 2,640,788
COATING CONTROL SYSTEM Filed Oct. 4, 1951 ERROR DETECTOR couu'rme RATE METER Mm I8 V CONTROL AMPLIFIER COMPARISON cmcurr STANDARD INVENTOR John F. Rockeh, Jr.
' qftor-ney' 4 Patented June 2, 1953 2,640,788 COATING CONTROL SYSTEM John F. Rockett, 'Jr., Medford, Mass., assignor to Columbia Broadcasting System, Inc., Salem, Mass., a corporation of New York Application October 4, 1951, Serial No. 249,773
This invention relates in general to methods for control of coatings being applied to objects and in particular to a method for maintaining desired characteristics in such coatings.
In many manufacturing processes it is desirable or necessary to provide a coating on an object for protective, ornamental, or functional purposes. In the case of functional coatings as, for example, when cathodes or heaters are being coated with materials having insulating or electron emitting properties, it is often necessary to hold the coating to a precise thickness or weight after it has been applied to the wire. Obviously, to obtain uniform characteristics in the finished product, it is important that the coating solution be maintained at the proper temperature, viscosity, or density depending upon the method being used to apply the coating. Also, the speed of passage of the uncoated wire through the coating station must be controlled to insure uniformity.
In the past, mechanical measurements with micrometers, calipers, depth gauges and the like have been widely used to check the thickness of the coating after application to a'surface. These techniques often required a periodic sampling of the output of the coating device with the usual disadvantages of wasted material and interruption of continuous production. Optical systems, for example, comparators and photoelectric devices have also been used fairly effectively where the shape of the surface permits a true indication of thickness to be obtained in that manner. Here, however, a troublesome element is usually encountered which limits the usefulness of optical devices, especially when thin wire or ribbon is being checked. When such material is continuously moving between reels or through other mechanical devices to pass it before the light source of the optical arrangement, a certain amount of vibration is usually present giving a false reading on thickness, the apparent thickness being larger because the vibrating material blocks a greater area of light than would a stationary member of similar thickness.
Therefore, it is an object of the present invention to provide an automatic monitoring system and method for accurately gauging the thickness per unit length of coating material being applied to a member.
It is a further object of the present invention to provide a method and a control system for maintaining a desired thickness of coating in response to the output of a monitoring device.
In general, the present invention consists in a system for passing a member consecutively through a coating station and a monitoring station. The coatingmaterial includes a minute amount of radioactive tracer material, and the basic element of the monitoring device is a counting rate-meter. Information obtained from the counting rate-meter is then fed back to the coating material station or to the drive for the member being coated and one or the other is varied as required to maintain the desired conditions in the coated member. For a better understanding of the invention together with other and further objects, features, and advantages which will become apparent, reference should be made to the following description which is to be read in connection with the accompanying drawing, the single figure of which is a block diagram of a drag coating system embodying several of the principles of the present invention.
Referring now to the drawing, there is illus trated a system for applying a controlled coating to a continuously moving wire. A supply reel II carries the uncoatedwire which is drawn therefrom by a wind-up reel I2. As the wire is drawn from supply reel II it passes through a drag coating bath l3. Coating bath 13 contains the coating solution and a small amount of distributed radioactive material. The contents of coating bath [3 are maintained within ranges of temperature, density and viscosity which are suitable to provide approximately the desired coating on the wire. As the wire emerges from coating bath l3 it passes before a counting tube I 4, the output of which is then displayed on a counting rate-meter l5 and also fed to a comparison circuit IS. The output of counting tube [4 then varies with the amount of radiation from the wire passing before it.
A standard source I! provides a second input to comparison circuit l6 and the two inputs are continuously checked against each other to provide an output error voltage to a motor control amplifier l8. The output from motor control amplifier I8 is then applied to a drive motor l9 which determines the speed at which the wire is drawn through coating bath l3, thereby determining the thickness of coating being applied to the wire. Although the present embodiment of the invention utilizes the radiation from the coating material to control speed, it is obvious that other parameters could be controlled in similar fashion. For example, the wire could be drawn at uniform speed and the density of the solution could be controlled by suitable solenoid valves triggered by the amplified output of the comparison circuit. Numerous applications of the concepts of the present invention to coating processes where controi of one or more parameters is desired will suggest themselves to those skilled in the art since the invention lends itself to incorporation in any closed-loop circuit wherein an error voltage is developed and used to diminish the conditions giving rise to-the error voltage,
For purposes of protection of personnel, the
is preferably one having a short half-life. Although a single reel of radioactive-wirewould constitute no hazard, the accumulat nfi -rceld radioactive material placed in coating bath l3.- first reel holding uncoated wire, a coating bath in continuous processing couldiprovide slifififiicnt.
emanation to reach the danger point. By using material having a short halt-life, this result is avoided since all harmful radiation disappears in a short time from such substances. Radioactive barium and strontium compound are suitable for use as tracers and are entirely. adequate for the required accuracy. evenwhen used with ccnventiona comme cial. d ecti n tru s Although the invention has been illustrated and described in connection with its incorporate tion inla cathode or heater. \vire coating device, the prinq ples of operation are equally applicable to any process wherein a member isto be coated, painted or otherwise covered with a material capable of carrying a distributed tracer. By a simple arrangement of controls or the addition orreorientation of cm nting devices control of diverse types of applying mechanisms can be achieved.
For the abovenoted reasons the invention should not be limitedto the embodiment shown which smereiy rpur ps s o p an t bu only by the app nded aims:
What. is claimed is:
1-. The. m ho oima nta n ng. ni o m t ickness. of a oatin heirs a p cd o a mo g. ir which, mprises thest ps o .addinaa at ly small. amount of. radicactir mate al. vin a relatively short halt-life to the coating substance, applyin thev radi a t ve. oating to th m i g wire te i the radiat on. om. he a d wire as t a es by a po nt om ar sth ected r diat nwiththat fr m st ndar isou and varying the speed'of said. moving wire in accordance with the difierence betweenthe radit o msa d tandard so r a th amount f diatio d t d:
2, Coating control apparatus comprising, a first reel holding uncoated; wire, a coating bath containing coating material anda minute quan- 4 tity of radioactive tracer material having a short half-life, a radiation detecting device, a wind-up reel to draw said uncoated wire from said first reel and consecutively through coating bath and past said detecting device, a motor for driving said wind-up reel, a standard source of radiation, and means responsive to the difierence between radiation from said standard source and that detected by said radiation detecting device for varying the speed of said motor.
3. Coating control apparatus comprising, a
containing coating material and a minute amountof radioactive tracer material having a shorthand-ire, a-icounting tube for detecting the strengthof radiation, a wind-up reel, means for driving said wind-up reel, mean-s for passing said uncoated wire from said first reel through saidcoatipg bath and past said counting tube to said wind-up reel, and means for controlling the speed of. said driving means in response to the output of. said counting tube.
.9 Appa a us fer coat n 1 W wmp si a supply reel for holding a quantity of uncoated wire, a coatingbath containing coating material and a minute amount .of distributed radioactive tracer having a. half-life of the order of. magnitude .of several hours, a radiation detecting counti g tube, a Wind-up reel, a motor. for drive ing said Wind-up reel whereby said wire is drawn from said supply reel,,through said coating bath and'past said'counting tube, a standard source for providing; a. predeterminedzamount ofradia tion, a comparison circuit for comparing the difference between the outputsof saidrcounting tube andsaid standard source, anda motor con-.- trol amplifier for continuously amplifying the ut ut of sai mpa s n rcu t, t e u putiof sa d mo or ont olamplifi r being pplied tosaid motor to control its speed and thereby. the rate of travel of said .wire the amountof coating nickecl p by s id ir being, ai ta ned substantial y nstant;
JOHN F. ROCKE'I'T, JR,
References Cited in the file of this patent UNI'IED STATES PATENTS Radioactive Isotopes as Tracers, Kramer Power Plantfingineering, Novemberi94'7, pgs. -108;