CONICITY CORRECTION FOR RUBBER COMPONENT EXTRUSION
A method for correcting the conicity of a tread strip is described. The method includes the steps of extruding a tread profile having a right hand side, a left hand side and a chimney; measuring the thickness of the tread profile at the right hand side and the left hand side; calculating the mass of the tread on the left hand side and the right hand side; and adjusting the location of the chimney incrementally towards the side which is least in mass.
This invention relates in general to extrusion, and more particularly to extrusion of elastomeric or rubber components, particularly treads for tires.
BACKGROUND OF THE INVENTIONIt 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 and corresponding to the desired specified green tread contour.
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. These imbalances are typically correctible by adjusting the contours in the flow channel and adjusting the performer and die dimensions. Dual tread extrusion has proven to be more difficult to manufacture two precise tread profiles at the same time where the contours of both tread extrudates match each other and match the green tread specification. The dividing of the rubber flow into two flow channels has the disadvantage of causing a more severe mass and velocity imbalance, which varies with the types and viscosity characteristics of rubber compounds selected. This problem may be partially addressed in the proper design of the dual cavity flow channel and allowing for proper flow channel lengths to allow disturbances to settle, before the compound reaches the die preformer.
In processing compounds for tire treads, there is batch-to-batch and day to day variations in compound viscosity. In treads processed on a properly designed single cavity tread extruder line, this typically results in treads being thicker or thinner than nominal specification at the center area of the tread, with very little net conicity variation. In the case of dual cavity tread extrusion, batch-to-batch and day to day variations in compound viscosity typically causes one tread profile to have positive conicity variation (too much mass) while the other tread cavity has negative tread conicity variation (too little mass). It is, therefore desired to provide a simple way of balancing the flow among one or more flow channels so that the proper side to side mass balance of the dual cavity treads is achieved. It is also desired to provide an adjustable means to compensate for mass variation and conicity variation within a profiled component.
With reference to
Each extruder 12, 14, 16, 18, 20, 22 typically includes an extruder screw 2 having an extruder tip 4 enclosed in an extruder barrel 3, as shown in
The rubber flow from flow passage 41,43 is each fed into its own preformer and die, commonly referred to as a profile die 46. The function of the flow channel 40 is to ensure that the elastomeric material is uniform in velocity and mass to ensure a uniform rubber strip exits the die. For dual tread extrusion, there is a tendency for the rubber flow to remain higher near the extruder head centerline of the flow channel than further away from the centerline of the channel. This results in each tread having a heavier portion on the “inside” or part of the tread closest to the centerline of the channel, as shown in
Next, the controller calculates the mass of the left hand side of the tread and the mass of the right hand side of the tread. If the mass on the left hand side and the right hand side of the strip falls outside the range of acceptable tolerances, then the controller will determine which side has a greater mass. If for example, the right hand side of the strip has a greater mass than the left hand side of the strip as shown in
Claims
1. A method for correcting the conicity of a tread strip, the method comprising the steps of:
- extruding a tread profile having a right hand side, a left hand side and a chimney;
- measuring the thickness of the tread profile at the right hand side and the left hand side;
- calculating the mass of the tread on the left hand side and the right hand side;
- adjusting the location of the chimney incrementally towards the side which is least in mass.
2. The method of claim 1 wherein the above steps are repeated until the calculated masses are within specification.
3. (canceled)
4. (canceled)
5. A method for correcting the conicity of a tread strip, the method comprising the steps of:
- extruding a tread profile having a right hand side, a left hand side, a cap, a base and a chimney;
- measuring the thickness of the tread profile at two or more locations;
- calculating the mass of the tread on the left hand side and the right hand side;
- determining if the left hand side mass is less than the predetermined left hand side specification and then moving the chimney to the right hand side;
- determining if the right hand side mass is less than the predetermined right hand side specification and moving the chimney to the left hand side.
6. The method of claim 5 further comprising the step of increasing the chimney width.
Type: Application
Filed: Jan 5, 2016
Publication Date: Jul 14, 2016
Inventor: Warren Paul RIPPLE (North Canton, OH)
Application Number: 14/988,174