TECHNICAL FIELD
This invention relates general to extrusion, and more particularly to extrusion of elastomeric or rubber components.
BACKGROUND OF THE INVENTION
It is known in the art of tire manufacturing to form tire components by extrusion. Typically, a strip of elastomeric or rubber material enters an extruder in solid pellet or strip form. The extruder typically has one or more internal screws in a heated barrel which perform work on the elastomer until it has reached a desired consistency. The elastomer exits the extruder and typically enters a flow channel comprised of one or more passages or channels that direct the plasticized material through the extruder head to an outlet or discharge die that forms the material into the proper predetermined cross-sectional profile. For example, if the material is a tread component, it is important that the formed profile of the tread be uniform in size.
It is a common practice in the rubber industry to use a single flow channel to extrude tire treads. Imbalances in the mass and velocity flow may occur, resulting in an uneven tread profile. The use of multiple channels for treads has been more elusive, since it has proven very difficult to make a uniform, precise extrudate required in today's treads. The dividing of the rubber flow into two symmetric channels has the disadvantage of causing a more severe mass and velocity imbalance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a top plan view of a first embodiment of an extruder flow head connected to an extruder on the upstream side of the material flow and to a profiling die on the downstream side of the channel flow. FIG. 1B shows the two temperature controlled zones in the flow channels, as well as the water flow paths for the temperature controlled water, which in turn controls the temperatures in the two flow channels temperature controlled zones.
FIG. 2 is a cross-sectional view of an elastomeric strip that has an uneven tread profile, where the tread is split into two half tread contours, C1 and C2.
FIG. 3 is a cross sectional view of FIG. 1 along its centerline.
FIG. 4 is a second embodiment of the present invention.
FIG. 5 illustrates a laser vision system;
FIG. 6 illustrates a flow chart describing a first embodiment of a conicity closed loop correction system.
FIGS. 7A, 7B, & 7C illustrates a flow chart describing a second embodiment of a conicity closed loop correction system, for a dual cavity tread extruder.
FIG. 8 illustrates a top plan view of a second embodiment of an extruder flow channel connected to an extruder on the upstream side of the material flow and to a profiling die on the downstream side of the channel flow.
FIG. 9 shows an improperly balanced tread profile.
FIG. 10 shows water passages and temperature controls for a dual cavity extruder head tongue.
FIG. 11 is a cross-sectional view of a hexaplex type, multiplex extruder.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIGS. 1a, 1b and FIG. 2 an extruder (partially shown) includes an extruder screw 2 having an extruder tip 4 enclosed in an extruder barrel 3. Attached to the extruder barrel is an extruder head 5. The extruder head 5 includes an internal flow channel 10 which has an inlet opening 30 for receiving plasticized material preferably elastomeric material from the extruder outlet. The flow channel 10 has an outlet opening 32 for discharging the plasticized material through a preformer and then a die for forming the profile of the elastomeric strip to be produced. This preformer and die combination is commonly referred to as a profile die 60 while the elastomeric strip is item 20 as illustrated in FIG. 2. The function of the flow channel 10 is to ensure that the elastomeric material is uniform in velocity and mass to ensure a uniform rubber strip exits the die.
FIG. 3 illustrates a cross-sectional view of the flow channel 10 in the direction 3-3. As shown, the flow channel 10 has a bottom wall 13 and a shaped upper wall 15. As shown in FIG. 1b, the flow channel 10 is divided into at least two temperature controlled zones: Tz1 (42) and Tz2 (44). The longitudinal axis 9 of the channel is preferably the dividing line between the zones. Each temperature controlled zone 42,44 is independently controllable with respect to temperature.
In the example of a single cavity tread extruder flow channel there are two separately controlled temperature zones. Each temperature controlled zone may comprise a coolant circulation system 45, 46 as shown in FIG. 4 formed of one or more circulation passages in the flow channel 10, along with coolant piping to a coolant circulation pump 49, 50, which circulates coolant through a temperature sensor 47, 48; a heating device 51, 52 (electric immersion heater or steam heated heat exchanger) and a cooling device 53, 54 (water to water heat exchanger). Each temperature controlled zone has a temperature controller 55, 56 which controls the starting and stopping of pumps 49, 50 and the heating or cooling of circulation coolant to a temperature setpoint received from the process controller 57 and with circulation temperature feedback from the temperature sensor 47, 48. Preferably, the coolant is water for ease of use. The invention is not limited to the heating or cooling devices, pumps, etc mentioned above, as other devices known to those skilled in the art may be substituted.
FIG. 5 illustrates a strip of elastomer 132 having an exemplary cross-sectional shape of a tread profile exiting the extruder head 5. FIG. 5 further illustrates a laser scanning system 100 for monitoring the tread profile characteristics. The laser scanning system 100 includes a laser 134 having a light beam that is dispersed by lens 135 into a sheet of light 122. The light sheet 122 has a field depth 133 and a field width 137. Reflected light 136 off of the exemplary tread profile strip 132 is reflected upward through a lens 138 and to a detector 140. The detector 140 functions to interpret in two dimensions the reflected light and generate data indicative of the dimensions and conicity of the target strip, by relating the gauges of the strip measured with respect to the centerline of the tread. From the scanning procedure, the dimensions (i.e., shape) and thickness of the strip is fed into the controller and compared with the specifications within a tolerance range on a continuous basis. If one or more of the dimensions on each side of the strip falls outside the range of acceptable tolerances, then the controller will appropriately adjust the temperature of each zone.
The side to side flow balance of the extruder flow channel, the preformer and the tread die determine the conicity of the uncured tread. For example as shown in FIG. 2, if one half of the tread “Contour C1” is thicker or heavier on one side as compared with the specification, the controller will cool or reduce the temperature of the temperature zone TZ142 by cooling the circulation water flowing through the water passages in that half of the flow channel. Reducing the temperature of the temperature zone which produces the heavier/thicker tread profile will result in a slower flow of elastomer, which has the effect of reducing the mass on that half of the tread.
If, on the other hand the thicker half of the tread, was at specified contours and the thinner half of the tread “Contour C2” was off specification, then the controller could heat or increase the temperature of TZ244, by heating the circulation water flowing in the water passages on that half of the flow channel. Increasing the temperature of the temperature zone which produces the lighter/thinner tread profile will result in a faster flow of elastomer, which has the effect of increasing the mass on that half of the tread. See FIG. 6 for the flowchart of the system logic describing the above.
EMBODIMENT 2
FIG. 8 illustrates a second embodiment of an extruder head to be mounted downstream of an extruder. The extruder head is the same as the extruder head of FIG. 1, except for the following differences. Between the inlet end 30 and the outlet end 32 of the flow channel 10, there are first and second flow passages 40, 50 respectively. Interposed between the first and second flow passages 40, 50, is a flow dam 12. The flow dam 12 is a flow splitter. The flow dam 12 separates the first flow passage 40 from the second flow passage 50. The flow dam can be used to extrude two rubber components, such as treads, at the same time.
There is a tendency for the rubber flow to remain higher near the extruder head centerline 9 of the flow channel 10 than further away from the centerline of the channel. This can be adjusted for in the design of the preformer and dies, to be used with a specific tread cap compound. However, in dual cavity tread extrusion, the natural variations in compound viscosity have the effect of creating positive conicity variations (ie, too much mass) in one tread and negative conicity variations (ie, too little mass) in the other tread. This is shown in FIG. 9—Treads T1 and T2. In this case, treads were produced with a tread cap compound having a higher viscosity than the compound used to develop the preformers and dies and as a result, the “tread halves” closer to the centerline of the head are heavier in gauge than specification, while the “tread halves” furthest from the centerline are lighter in gauge than the specification. The overall tread weights of the treads meet specification. This is due to the fact that the higher viscosity compound did not flow away from the head centerline, as was the case when the preformers and dies were developed.
In order to correct this flow imbalance, the flow channel is divided into three temperature zones as shown in FIG. 10. The first temperature zone 200 is located on one of the outer portions of the flow channel (FIG. 8—TZ1) and affects the outside portion of tread T1, shown in FIG. 9. The second temperature zone 210 (FIG. 8 TZ2) is located in the middle of the flow channel and affects the inside portion of Tread T1 (contour C2) and the inside portion of Tread T2 (contour C1), shown on FIG. 9. The third temperature zone 220 (FIG. 8 TZ3) is located on the other outer portion of the flow channel and affects the outside portion of Tread T2, shown in FIG. 9. In order to correct the flow imbalance shown in FIG. 9, the middle temperature zone 210 is cooled from its nominal running specified temperature. Temperature zones 200 and 220 may also be increased in temperature (from the nominal specification) to increase the flow to the outside “tread halves”, so that the side to side tread masses and resulting conicities are balanced to be back to specification.
Referring now to FIG. 11, a hexaplex extruder head 300 is shown, which has a head “tongue” 301. The head tongue and flow channel 302 guide the rubber flow from extruder #2303. The head tongue and flow channel 304 guide the rubber flow from extruder #3305. By drilling water passages in the extruder tongue and controlling the temperature of the water flowing in those water passages, it is possible to affect the flow characteristics of the rubber being extruded by both extruder #2, 303 and extruder #3, 305 simultaneously. As extruders 303 and 305 are the extruder positions typically used to extruder cap compounds, these extruders produce the largest portion of mass in treads.
Refer to FIG. 10. FIG. 10 shows the coolant passages drilled into an extruder tongue and the controls scheme for controlling the coolant passing through three sets of coolant passages in the head tongue. This extruder tongue is designed for operation with a dual cavity tread extruder. The tongue is broken up into three distinct temperature zones 200, 210, and 220, corresponding to the temperature zones identified on FIG. 8. The controls for each temperature zone include a circulation coolant temperature sensor (232, 242, 252), a coolant circulation pump (233, 243, 253) a circulation coolant heating unit (234, 244, 254) and a circulation coolant cooler (235, 245, 255) all interconnected to a temperature controller (231, 241, 251). The temperature controller in each temperature controlled tongue zone maintains a temperature setpoint received from the process controller by comparing the setpoint to actual coolant temperatures received from the circulation coolant sensor and controlling the coolant circulation pump and the circulation coolant heating and cooling units.
Patent Application
20130154142
