Conditioning System for Water Based Can Sealants

The present invention relates to a system for conditioning water based can sealants. More particularly, it relates to a system for controlling the film weight of a water based can lining compound in a lining system.

There are two basic groups of can lining compounds in use today; solvent based and water based.

Solvent based compounds comprise a rubber based can lining compound dissolved and/or dispersed in one or more solvents. After the compound is lined onto a can end, the solvent is driven off to leave a resilient gasket.

Water based compounds are similar, however, the compounds are dispersed and/or emulsified in water rather than a solvent. These materials therefore avoid the problems normally associated with solvents, such as pollution, flammability, and health effects.

Typically, both compounds are supplied under pressure to a lining nozzle. A can end, mounted to rotary chuck below the nozzle, is rotated at a set speed. The nozzle is opened to apply the required amount of compound to the can end.

The key to obtain an acceptably lined can end is the sufficient and consistent deposition of compound as defined by the film weight and placement of the compound on the end. Film weight is the amount of compound that is applied to each can end. If too much is applied, the excess compound could distort the seal causing leakage, compound is wasted and the profitability suffers. If too little is applied, the end will not form a proper seal and leakage occurs.

Film weight can be approximately determined by the following equation: ##EQU1## where FW is film weight, P is the pressure difference between that contained within the lining system and the atmospheric air pressure, D is the diameter of the lining nozzle orifice, .eta. is the viscosity of the compound as it flows through the nozzle, L is the lead length of the nozzle, and t is the lining time. This equation has been simplified and does not take into account other variables such as the wear of the nozzle, the configuration of the inside surface of the nozzle (tapered, etc.), the height to which the nozzle needle is lifted during lining, transient flow response from needle opening/closing, and elastic response of the compound. However, these variables are secondary in their effect and can, for purposes of this discussion, be ignored.

For a manufacturer of can ends, D and L are fixed for a given nozzle. Pressure and viscosity tend to vary depending on environmental effects on the system. Pressure and viscosity must be controlled and held constant in order to obtain consistent and sufficient film weights.

In solvent systems, the pressure and temperature are regulated by a "conditioner". This conditioning system comprises a rotary gear pump, a filter and a heater connected to the supply side of a lining nozzle and a back pressure regulator or pinch valve connected between the exit side of the nozzle and the gear pump. Gear pumps have steady flow and discharge pressure. Constant pressure in the system is required to maintain consistent film weight. In order to preclude a fluctuation in pressure each time the lining nozzle is opened, the recycle system is designed to recirculate large amounts of compound, usually 40 to 50 times the amount discharged through the nozzle. The heater is thermostatically regulated such that the temperature of the compound in the conditioner is closely controlled. As a consequence the compound viscosity, which is temperature sensitive, is accurately maintained. If the lining system should become inoperative for an extended period of time, the compound could make hundreds of passes through the recycle system. This amount of recycling is not a problem for solvent based compounds which are generally thermodynamically stable products.

However, water based compounds, being emulsions and/or dispersions, are not thermodynamically stable. Water based compounds require the use of surface active agents or protective colloids to maintain the compound in a usable state until lined.

The close clearances associated with rotary pumps cause a great amount of shear stress on water based compounds which destabilizes the compound, thus precluding the use of a conditioning system as is used in solvent based compounds.

This inability to condition water based compounds causes problems to the can end manufacturer in controlling and obtaining a consistent film weight. Fluctuations in ambient temperature which frequently occur on a daily basis, shutdowns during which the viscosity of the compound increases and the inability to hold the compound at a constant pressure precludes can end manufacturers from controlling film weights at +/-10% of the desired weight, which is the standard for solvent based compounds. Field experience has shown that controlling film weights even at +/-15% of the desired weight is often difficult to achieve with water based compounds.

The present invention overcomes the difficulties encountered with lining water based compounds and greatly improves the film weight control of water based compounds.

The present invention is a system for conditioning water based compounds such that consistent film weights can be applied to can ends. The system comprises a downstream regulator or alternatively a gravity feed supply tank connected to the compound supply, a pump connected to the opposite side of the downstream regulator or gravity feed supply tank, a filter and a heater connected between the pump and the lining nozzle, and a back pressure regulator connecting the exit port of the lining nozzle to the inlet of the pump. The preferred embodiment uses a double diaphragm pump and contains two pressure pulsation dampeners, one located downstream from the pump and the other located downstream from the back pressure regulator. The conditioning system of the present invention allows film weight control within +/-5%. The preferred embodiment of the present invention provides even further control to within +/-3%.

FIG. 1 is a representation of an embodiment of the present invention.

FIG. 2 is a representation of the preferred embodiment of the present invention.

FIG. 3 is a representation of another preferred embodiment of the present invention.

FIG. 1 shows an embodiment of the present invention. The details to the left of the dotted line represent the can end manufacturer's plant. A supply 1 of compound from the manufacturer's storage is passed through a valve 2 and filter 3 and past drain valve 4 and into the conditioning system. A first pressure regulation means 5, preferably a downstream regulator is provided near the connection of the supply to the system. A means for sensing pressure in the system, preferably a pressure gauge 6 is located downstream from the regulation means 5. A pumping means 7, preferably a diaphragm type pump is located downstream from the pressure gauge 6. The pumping means discharges into a filtering means 8 for collecting coagulum that may form in the system. A drain valve 9 and a valve 10 are located between the filtering means 8 and a temperature controlling means 11 for the compound. The temperature controlling means is connected to an inlet port 12 of a lining nozzle 13. The compound which is not lined through the nozzle 13 is discharged through an outlet port 14. A pressure gauge 15 located downstream of the outlet port 14, monitors the lining pressure of the system. A second pressure regulation means 16 is located downstream from the pressure gauge 15. Preferably, it is a back pressure regulator, although a pinch valve or other restriction may be used as well. An additional drain valve 17 and valve 18 are located downstream from the second pressure regulation means 16 and are connected to the system between the first pressure regulation means 5 and the pump 7 by a return line 19. All of the various components are connected to each other by appropriate conduit means such as metal or plastic tubing or piping.

FIG. 2 shows a preferred embodiment of the present invention connected to a can end manufacturer's equipment. The supply 20 is connected to a pressure gauge 21 which connected to a valve 22 and a filter 23. A second pressure gauge 24 is located downstream of the filter 23 and adjacent a drain valve 25. The use of gauges 21 and 24 allows one to monitor the function of the filter 23.

A downstream pressure regulator 26 is connected to the manufacturer's supply line. This regulator is upstream of the pump 28 and the return line 47 from the nozzle 38. The pump 28 is then connected to a first dampening means 29 for damping any pressure fluctuations caused by the pump 28 or other components in the system. The dampening device 29, as shown, may be attached by a valve 30 so that it may be selectively actuated as desired and easily removed should the device require maintenance. Preferably, a pressure gauge 31 is mounted to the dampening means 29. A filter 32 is located beyond the dampening device. A drain valve 33 and valve 35 are used to control the flow of the system as required. A pressure gauge 34 is located between the valves 33 and 35 to monitor filter function. Beyond the valve 35 is a heater 36 for warming the compound to the desired temperature. The function of the heater is to maintain a constant compound temperature in the event of an ambient temperature variation in the plant. The heater 36 is connected to the inlet port 37 of the lining nozzle 38. Unlined compound is circulated through the nozzle 38 and out exit port 39. Lining pressure is monitored by pressure gauge 40. The pressure of the system is regulated by the back pressure regulator 41 adjacent the pressure gauge 40. A second dampening means 42 is connected by a valve 43 downstream from the back pressure regulator 41. As shown, the preferred dampening means has a pressure gauge 44 attached to it for monitoring of the dampening system. A drain valve 45 and a valve 46 are located downstream from the second dampening means 42 and are used to control the flow of the system. A return line 47 is attached to the system between the downstream regulator 26 and the inlet side of the pump 28 to allow for the recirculation of compound.

The use of a gravity feed tank to supply the system is an alternative embodiment to the use of a first pressure regulator as shown in by the embodiments of FIGS. 1 and 2. This is a useful alternative particularly where the first pressure regulator is designed to compensate for these supply pressure variations and hold the feed pressure to the pump constant. As the regulator wears, leakage paths can develop which reduce the ability of the first regulator to respond fully, especially during periods in which the lining machine is down where tight shut off is desired.

The gravity feed tank is preferably attached to the manufacturer's supply by an automatic valve. The valve is also attached to a level sensor mounted adjacent the tank. The sensor measures the level of compound in the tank and thus controls the actuation of the valve supplying compound to the tank. Various sensors are well known and widely used for controlling the level of fluid in a container.

For example, a float may be used which mechanically or electrically operates the valve. When the compound level reaches a lower predetermined limit in the tank, the float opens the valve and allows compound to flow into the tank. When the float has risen to a predetermined upper level, the float will shut off the valve, stopping the supply of compound to the tank.

Another suitable sensor is known as a conductivity probe. In this embodiment there are generally two such probes, one which senses the preset lower limit and another for sensing the upper limit for the tank.

More preferably, the sensor is not immersed in the compound within the tank. It has been found that when the sensor, such as a float or conductivity probe, is immersed in the compound, the compound tends to adhere to the sensor over time, thus reducing the sensitivity and the reliability of the sensor.

One preferred level control device is a series of capacitance sensors which are preferably located on the outer surface of the tank. (Although if desired, one may mount the sensors on the inside wall of the tank). Preferably, three sensors are used, one to open the valve when the level reaches a desired lower limit in the tank, a second one to close the valve when at a high preset level and a third located above the second which acts as a failsafe to shut down the conditioner and sound an alarm. With the use of such sensors on the exterior of the tank, it is believed that a metallic tank cannot be used. A plastic tank is preferred although a glass or a composite type of material may also be used. Additionally, although compound may eventually coat the side of the tank, the selected sensors preferably would be tunable so that the effects of any such coating can be eliminated.

Another preferred level control system consists of an ultrasonic sensor mounted on the inside of the tank but above the desired upper liquid level. The ultrasonic sensor determines the level of the fluid in the tank through the use of sound waves and opens and closes the valve accordingly. Preferably, a failsafe sensor is also mounted near the ultrasonic sensor in the event of a failure of the ultrasonic sensor. The ultrasonic sensor may be used in a metal tank or a plastic, glass or composite tank.

Capacitive sensors are well known and widely available. Such a sensor can be purchased from Industrial Sensors, Newport, Mich.

An ultrasonic sensor that is preferred in the present invention can be purchased from Industrial Sensors, Newport, Mich.

Another method of dealing with the issue of wear in the downstream regulator as the first pressure regulating device is to use a rubber ball instead of a metal one in the regulator. The rubber will cold flow and conform to the seat as the ball wears. The use of the rubber ball greatly extends the effective life of the ball and seat.

Additional features may also be added to the system as desired. For example, in the event that the lining system is shut down, e.g. for problems incurred in the supply of container closures or for other problems incurred in components not contained within the conditioning system, it would be advantageous to incorporate a signaling system between the lining system and the conditioning system so as to close off the compound supply to the first regulation device. One could incorporate an automatic shut off valve to the compound supply so that if a problem occurs with any of the other systems which interact with the conditioning system (e.g. lining system, closure supply and transportation system, etc.) the supply of compound to the conditioner system is shut off.

The above automatic shut off valve would preclude compound from bleeding past the first regulation device if it should become worn thus further extending the useful life of the first regulation device such that it can operate effectively even after substantial wear occurs. Likewise this same shut off valve could be actuated if the air pressure supplied to the conditioner is lost or drops too low thus protecting the diaphragms of the pump and bladders of the pulsation dampeners from high differential pressure that can result if compound should bleed past a worn first pressure regulation.

A preferred sensor could control a solenoid which could actuate a valve located in the compound supply line between the manufacturer's supply and the beginning of the conditioning system such that upon a signal from the sensor, the compound supply would be shut off and/or the conditioning system shut down. Another preferred embodiment is to use a sensor and electrically actuated valve.

The pumping means of the system is a pump, the moving parts of which operate at relatively low velocities and which have large clearances so as to have little shearing effect on the compound as it circulates through the system. This prevents the viscosity and stability of the compound from being adversely affected as it is cycled. A preferred pump is a diaphragm type pump. More preferably, it is a double diaphragm type of pump.

In addition to the low shear imparted to the compound, diaphragm pumps are preferred as they do not exhibit seal problems due to friction and wear as is common with piston type pumps, progressive cavity pumps, lobe pumps, etc. which can be used to pump water based compounds. Additionally, these pumps, particularly double diaphragm pumps, tend to generate smaller pressure pulsations than single diaphragm pumps, thus reducing the pressure fluctuation that must be damped. Lastly, because of the mild shearing stresses, these pumps do not tend to form coagulum which could block the system.

Preferably, the selected pump has a low volumetric displacement/stroke so as to further minimize the magnitude of the pulsations. Additionally, the chosen pump should be selected so that it can cycle a sufficient volume of compound through the system to avoid significant fluctuations in the circulation compound volume due to the discharge of compound at the nozzle. The pump preferably should be able to cycle a volume of compound that is from about 10 to 60 times the amount of compound discharged through the nozzle. Typically, this would require a pump capable of pumping 0.1 to 0.6 gallons/minute.

Additionally, the preferred pump will have diaphragms made from polytetrafluoroethylene or other flexible materials with a low coefficient of friction and a body formed from plastic such as polypropylene or a metal such as stainless steel, so as to reduce the tendency for having coagulum that might be formed to remain inside the pump.

One such pump is sold by Yamada American, Inc. While the named pump is air actuated, other mechanically or electrically driven pumps could also be used.

The filter may be any filter commonly used in compound lining equipment including basket type fillers, pleated filters, etc. Preferably, the filter used in the system consists of a stainless steel wire mesh screen having a mesh opening of 40 per inch and which is contained with a basket type housing. Such a filter can be obtained from The Kraissl Co. of Hackensack, N.J.

The first pressure regulating means may be a downstream pressure regulator, e.g. a regulator that senses the pressure of the fluid downstream from its position and actuates according to changes in that pressure. This regulator tends to reduce pressure flucuations that may be received from the can end manufacturer's supply system. Such a regulator is commercially available from the Aro Corporation of Bryan, Ohio.

Alternatively, the first pressure regulating means may be a gravity-fed tank system as described above. The tank may have an open top or alternatively it may be a closed tank. If the latter, a vent should be provided in the top of the tank. The tank should have at least one inlet, preferably located near the top of the tank and one outlet located near the bottom, preferably the bottom of the tank.

Alternatively, the tank may have a movable bellows or diaphragm which moves relative to the volume of fluid in it so as to maintain the same pressure on the compound.

Other alternative embodiments for such a closed tank system include a level sensing device which operates over a very narrow range of levels so as to reduce the air flow in and out of the tank thus reducing the possibility of skinning or coagulation. Likewise, the use of large volume tank (i.e. large head space) and relatively small amount of movement of the fluid and/or bellows or diaphragm may also be used.

It is preferred that whatever system is selected, it not compress the air in the head space of the tank to any significant degree and thereby not vary the head of the fluid by any appreciable amount. By minimizing the fluctuation in head of the fluid, one reduces the pressure variation on the compound supply to the pump.

The second pressure regulation means is a back pressure or upstream pressure regulator. It operates in a manner similar to that of the downstream regulator, except it responds to the pressure changes of the compound upstream from the regulator. In this instance, the back pressure regulator responds to changes in the line pressure between itself and the exit port of the lining nozzle. Alternatively, a pinch valve or other restriction may be used instead of the second pressure regulator.

A suitable back pressure regulator is also available from the Aro Corporation.

The purpose of the pressure regulators is to maintain the lining pressure of the system at a constant value. The preferred size of the regulator should be matched to the desired range of operating pressure and the desired flow rate of the compound in the system. The back pressure regulator does, in addition, apply a controlled shearing action to the compound to break down any structure that may have formed.

The pair of regulators have a synergistic effect on each other and the system. It has been found that should the first regulator lose sensitivity, the other regulator is able to compensate and regulate the pressure within the system.

It is preferred that the temperature of the compound in the conditioner be controlled so that the film weight can be kept constant. Compound viscosity is affected by temperature, however, if desired, one may not use a temperature control means in the present invention. In particular, such a control means is not necessary when the ambient temperature can reasonably be controlled within the plant, such as by plant air conditioning or heating systems.

The means for controlling the temperature of the compound is preferably a heater with a controller having a variable set point. More preferably, the heater comprises a tube through which the compound circulates and which is heated from the outside by fluids, hot air, electrical resistance and other well known heating means. One such heater comprises a flexible tube, formed of polytetrafluoroethylene or other such materials with a low coefficient of friction so as to reduce the chance of coagulum being trapped in the heater, which is surrounded by a jacket having heating wires or coils mounted therein. Such a heater is capable of raising the temperature of a compound in the system by 20.degree. F. above the outside ambient temperature within 30 minutes without excessive jacket temperatures and maintaining that temperature while the system is in operation.

One such heater is available from Omni Systems of Frenchtown, N.J. and comprises a 3 foot tube of 3/8 inch (internal diameter) hose formed of polytetrafluoroethylene. The hose is surrounded by a jacket having electrical heaters (30 watts per foot) and is thermostatically controlled.

The first and second damping means are preferably pressure surge suppressors which minimize and even out pressure fluctuations in the system. One preferred surge suppressor has a bladder that separates a chamber into two parts and a regulator for the introduction of air into the upper portion of the chamber. Compound from the system flows into the lower portion of the chamber. As the level of the fluid moves up and down in the chamber due to pressure fluctuations, the regulator automatically permits air to flow into the upper portion of the chamber as is required to damp the pressure pulsation.

Other types of surge suppressors or pressure dampeners may be known and are useful in the present invention. For example, the pressure dampener may be a fixed charge type of bladder dampener or a flow through type of dampener. A fixed charge bladder dampener is similar to the preferred variable charged dampener, however there is no regulator for the introduction of additional air as the bladder expands or contracts. Additionally, one may use an additional downstream regulator in lieu of the dampener to obtain the same effect. Also, one may use a flow control valve which controls the flow of the compound rather than the pressure of the compound and obtain the same result.

The damping means in FIG. 2 is shown with a pressure gauge. While it is preferable that the dampener have such a gauge, it is by no means required.

One suitable dampener is sold by Wilden Pump and Engineering under the name Blacoh Sentry II (automatic version).

It is preferred that two dampeners be used in the present system, although it has been found that one dampener located on the downstream side of the pump is sufficient in some cases to damp pressure pulsation. The additional dampener located downstream from the back pressure regulator tends to minimize any water hammer effect that might occur to the pump by the pressurized feed of compound. This tends to increase the efficiency of the system and extend the useful life of the pump.

Additionally, one may add a pressure regulator, as described above, between the pumping means and the lining nozzle or nozzles. The addition of this regulator eliminates any pressure flucuation in the system, particularly when one is not using the preferred double diaphragm pump. Alternatively, one may use a flow control valve instead of the additional downstream regulator. In this instance, the flow of compound rather than the pressure is maintained constant. The addition of one or more pressure regulators or flow control valves is of particular value when one wishes to supply two lining nozzles from one conditioning system.

It is preferred that each of the components of the system be connected by easily detachable means such as threaded couplings, etc. to allow disassembly of a portion of the system when maintainance or repairs need to be made.

The piping or tubing used in transporting the compound through the system can be constructed of any material that is commonly used with water based compounds. The tubing should be inert to the compound, strong, long lasting and preferably inexpensive. Typical materials include steel, particularly 304 stainless steel, aluminum and various plastics such as CPVC (chlorinated polyvinyl chloride) and high pressure polypropylene pipe and fittings. These plastics are preferred as they do not loose appreciable strength at the temperatures encountered in the system.

The system may also contain various pressure sensors and/or temperature sensors which may be displayed upon a control board so as to allow an operator to determine the exact condition of the system at any time. If desired, such sensors can be wired to an alarm so that if a malfunction occurs, the operator is instantly notified and remedial action can be taken.

Once the system has been connected to the manufacturer's supply line and lining nozzles and provided with the appropriate electrical and pressurized air supplies, the system is filled with compound, purged of air, and brought to operating temperature and pressure.

The system is then essentially automatic and should only be monitored for changes. Changes in compound temperature and thus compound viscosity are obtained through varying the temperature of the heater temperature is usually set about 5.degree. to 10.degree. F. above the maximum ambient temperature expected. Changes in lining pressure are obtained through adjustments to the back pressure regulator, the pump air pressure is set initially and need not be adjusted thereafter.

Compound from the supply will be drawn, as needed by the system, through the downstream regulator and into the pump. The compound then flows through the first dampener, filter and heater to the lining nozzle. There a portion of the compound is discharged onto the can end. The remaining compound is recycled to the pump where it begins its next cycle.

In the event that the lining nozzle is closed for an extended period of time, such as may occur when the supply of ends to be lined is interrupted the conditioner system may continue to circulate compound and upon restarting of the lining nozzle, the conditioner will provide consistent film weights to the can ends. In the embodiment of FIG. 2, a commercial compound was cycled through the system for 42 hours without draw off (approx. 2000 cycles). The reduction in viscosity of the compound was insignificant. Mechanical stability and other lining characteristics of the compound were essentially unchanged. This test represented an abnormal and extreme situation. Most shutdowns will last from 10 minutes to a few hours and under these circumstances, negligible change in viscosity of the compound will occur. If desired, one can alternatively shut down the conditioning system when the lining equipment is inoperative for more than a couple of hours and activate the system when the lining equipment is started again. For particularly sensitive compounds, it may be prudent to do so.

While this invention has been described in relation to a one nozzle lining system, it should be pointed out that more than one nozzle may be run from the conditioning unit of the present invention.

To attach two nozzles to the system, one would merely need to divide the compound flow at some point between the pump and the nozzle so as to provide two compound supply lines to the two nozzles. The two nozzle outlet ports would then be connected to a common supply line before the second pressure regulation means. Preferably, the compound supply line is separated into two channels just before the lining nozzle inlet ports so that additional heaters (if used) filters, etc. are not required.

If independent pressure control of each nozzle is desired, one may do so easily by adding a downstream regulator or flow control valve to each branch of the tubing adjacent the inlet port to each gun. Additionally, an upstream pressure regulator should be used on each the outlet port of each gun rather than using a common one as described above.

FIG. 3 shows an embodiment of the present invention which incorporated the gravity feed system and the multigun, independently controlled features of the present invention. FIG. 3 is essentially identical to FIG. 1 except for various added or changed features. In particular, FIG. 3 shows the manufacturer's supply of compound 101 supplied through a valve 102 and filter 103, past drain valve 104 and into the conditioning system. The compound flows through a valve 105 which is controlled by level sensing device 106 adjacent to or incorporated into the gravity feed tank 107 as the first pressure regulating means. The compound is fed to the tank by an inlet 108 and drawn out of the tank 107 from the bottom by an outlet 109. From there, the compound flows through the pump 110, filter 111, past drain valve 112 and through valve 113 to the heater 114 (optional). After the heater 114, if used, the line is split into two separate loops at a junction 115. Compound then flows through the parallel lines 116A and B and downstream regulators 117A and B and into nozzles 118A and B. If desired, one may add shut off valves in each branch to allow one to balance the flow in the branches.

If either valve is activated, the compound flows through either nozzle 118A or 118B or both. That compound which is not drawn out through nozzles 118A or 118B flows out the respective outlet port 119A or 119B, past a second pressure regulating device, in this embodiment on upstream regulator, either 120A or 120B, to the junction point 121 where the two compound flows are reunited. From this point, the compound flows past drain valve 122, valve 123 to return line 124 to the pump 110 for recirculation.

By using a pressure or flow regulating means on each side of the respective nozzles 118A and 118B, one is able to maintain constant pressure, shear history, temperature, etc. throughout the entire system even though one or both of the nozzles may be actuated, simultaneously or not and change the pressure in one branch or to one gun without affecting the other.

One could of course use a flow control valve in lieu of the downstream regulators, if desired.

The present invention provides several advantages to the manufacturer of can ends.

Most importantly, it provides improved film weight control without compromising the mechanical stability, flow and sealing properties of the compound.

Moreover, one can control film weight by needle lift adjustment only or by pressure adjustment as well, although the balance between the branches may be offset.

Additionally, manufacturers do not have to be concerned about ambient temperature variation, compound shear history or variations in supply pressure as the conditioner maintains the compound at a constant temperature, pressure and viscosity.

It is known that changes in ambient air temperatures can cause a fluctuation in the film weight obtained from a system. In general, the film weight will vary by about 1% per .degree.F. Therefore, a change in temperature of 20.degree. F. during the course of a day, which is not uncommon in most parts of the world, would result in a deviation in film weights of up to 20%.

Likewise, a change in line pressure is known to affect the film weight. In general change of 1 psi will cause about a 4% change in the film weight obtained, when the lining pressure is in the range of 20 to 30 psi, which is typical of commercial conditions.

Compound viscosity is affected by shear history, especially shutdowns, which can occur randomly or during scheduled maintenance checks or on weekends.

The present invention is unique in that it controls the effects of pressure, temperature and shear history (since the most recent shear history is dominant on the system) and provides consistent film weights despite changes in the ambient temperature, supply pressure or shear history upstream. It has been determined that the present invention allows control of compound temperature to within +/-1.degree. F. of the desired temperature. Additionally, the present invention allows control of compound lining pressure to within +/-0.5 psi of the desired pressure level when the lining pressure is in the range of 20-30 psi. With such sensitive control, the present invention has been able to negate the effects of ambient temperature, supply pressure and shear history on the film weight of the compound.

Additionally, the present invention allows the can end manufacturer to vary the temperature of the compound within the system and gain additional control in adjusting proper placement of the compound on the can end. Varying the temperature of the compound within the system changes its viscosity and thus provides a different flow out of the compound as it is lined on the can end. In this manner placement of the compound on the can end can be altered by varying the temperature in the system.

The present invention also allows the compound manufacturer greater latitude in selecting the flow characteristics of the compound. Compound is preferrably manufactured with a yield value so that the various components of the compounds do not settle out during transportation and storage. Unfortunately, the yield value may affect the flow of the compound at moderate and high shear rates as occur in the supply piping and lining nozzles. Compounds generally represent a balance between the characteristics at low shear rates, moderate and high shear rates.

The present invention, due to its control of temperature and pressure and shearing action, allows the compound manufacturer to vary the low shear rate characteristics to a greater extent as the system allows the can end manufacturer to vary the viscosity of the compound in the system. Moreover, as shown in FIG. 3, the present invention allows a can end manufacturer to independently control the function of two or more lining nozzles from one conditioning system, thus making the system more economical to use.

The present invention, due to its ability to provide consistent film weights, allows the can end manufacturer to reduce the target film weight of the compound without risk of rejecting increased numbers of can ends. As film weights currently vary by +/-15%, a target film weight must be at least 15% higher than desired so as to compensate for low film weight deposition. As the present invention provides a means for accurately controlling film weights, the can end manufacturer may reduce his target film weight significantly without adversely affecting rejection rate, thus increasing profitability.

In summation, the system, without any specific damping means, is capable of damping the pressure fluctuations of the system to an extent that film weight can be controlled to within +/-5% of the desired weight. This is a two fold improvement in film weight control over that currently achieved in solvent compound systems and a three fold improvement in film weight control over that currently achieved in water based compound systems.

With the use of at least one damping means, the system provides film weights within +/-3% of the desired weight. When both damping means are used, the film weight is controlled to within +/-3% of the desired weight, and additional advantages are obtained, such as reduction in the water hammer effect with a pressurized feed, thus extending pump life. The use of the one or more dampeners represents a five fold improvement in the ability to control film weights as compared to that currently achieved with water based compound systems.

While the present invention has been disclosed with reference to its preferred embodiments, other embodiments can achieve the same result. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended in the appended claims to cover all such modifications and equivalents as fall within the true spirit and scope of this invention.