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Regardless of the technology that you use in your facility- you have a control system. If this is a man with 15 years of knowledge, or a kid with a clipboard and discrete controls, or an automated solution – you have a system.

The principal function of ANY control system involves the monitoring and control of a wide variety of process and product parameters.

• Barrel Temperatures
• Extruder Speeds
• Melt Temperature
• Melt and Screen pressures
• Drive Load
• Coordinated Feeders
• Coordinated Down Stream Drives

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• Are the settings optimal?
• How does one setting affect another?
• Are we sure they are set at the right points?
• What if our operator leaves for a competitor?
• Can we trust each shift of operators to operate the same way?
• Are we sure that settings are adjusted between products appropriately?

All of these questions are answered- with great benefit, with an automated control system. A centralized operator interface allows the operator to MANAGE through a consolidated view of the process, and not just respond to it.

Extrusion Control Points

• Blending ratios of multiple ingredients
• Extruder throughput in lbs/hour or lbs/ft
• Extruder barrel temperature zones – These are usually have heating & cooling
• Tooling temperature zones – These are usually heat only
• Die temperature zones – These are usually heat only
• Speeds
• Extruder screw
• Roll stands
• Pullers
• Conveyors
• Capstans
• Wind-ups
• Tension – product tension is controlled by varying the appropriate speed(s) based on load cell or dancer feedback
• Melt Pump Inlet Pressure
• Product Dimensions
• OD (outside diameter)
• ID (inside diameter)
• Width
• Height
• Wall Thickness
• Roll Length
• Cut-to-Length

Parameters typically monitored in the extrusion:

• Drive Loads
• Melt Temperature
• Melt Pressure
• Tension
• Cut Counting
• Product Dimensions

Recommended additional parameters for monitoring to detect problems before any damage occurs, track for maintenance purposes, or assure proper process conditions:

• Gear Box Temperature, Pressure, and Lube Flow
• Motor Temperature
• Drive Faults
• Cooling Tank Temperature
• Relative Humidity and/or Dew Point – controlling cooling roll temperatures to just above the dew point can prevent corrosion and contamination of the product with moisture
• Moisture of Raw Material

Operator vs. Computer

Regardless of the technology that you use in your facility- you have a control system. If this is a man with 15 years of knowledge, or a kid with a clipboard and discrete controls, or an automated solution – you have a system.

The principal function of ANY control system involves the monitoring and control of a wide variety of process and product parameters.

• Barrel Temperatures
• Extruder Speeds
• Melt Temperature
• Melt and Screen pressures
• Drive Load
• Coordinated Feeders
• Coordinated Down Stream Drives

A human operator using discrete controls can adjust all of these control points to workable settings, however the questions remain:

• Are the settings optimal?
• How does one setting affect another?
• Are we sure they are set at the right points?
• What if our operator leaves for a competitor?
• Can we trust each shift of operators to operate the same way?
• Are we sure that settings are adjusted between products appropriately?

All of these questions are answered- with great benefit, with an automated control system. A centralized operator interface allows the operator to MANAGE through a consolidated view of the process, and not just respond to it.

The best approach is to derive the management information as a by-product of the automation of the equipment. Which can be done. (and FACTS does every day)

Continued information automation of the world’s rubber and plastic industries- both the multi-national corporations AND the mom-and-pop manufacturers, will allow for the following:

• Co-ordinate and control the complete production line
• Analyze and optimize the process
• Track in ‘Real Time’ all production status
• Report on good product produced, scrap, and raw material usage
• Manage the overall production process
• Download job schedules directly to the floor system
• Provide the operator with quality information
• Minimize inventory
• Maximize productivity
• Provide end user documentation to assure they are receiving quality products made to their unique specification

All of these things are crucial in minimizing the personnel required to produce product, and providing full plant-wide visibility for management.

Localized cord disturbance in cord distribution does not usually affect fabric weight, whereas overall cord distribution problems can affect fabric weight, sheet gauge, and quality.

For example, an incorrect cord distribution that has a light weight center and heavy outer edges is due to:

• reduced average EPI (Ends per Inch) in the center of the fabric and
• increased EPI on the outer edges

How can this happen? -I’ve got a scanner!!

First, off:

• Weight samples alone do not distinguish between cord & gum
• Thickness samples alone do not distinguish between cord & gum
• Thickness & weight still do not distinguish between cord & gum
• Cord count must always be considered

A scanner is an excellent tool for the operator but is not necessarily recommended for control.

Here’s the problem

Many 4 Roll Calenders have space limitations that have prevented the use of on-calender gauges on the top gum wall. Historically this has necessitated the use of on-calender gauges on the lower gum wall and an overall scanner with math derivation of the top gum profile. This has lead to many calenders producing off-spec material that had a flat weight & thickness profile. Cords tend to bunch on the outer edges and have reduced EPI (Ends Per Inch) in the center.

The scanner cannot distinguish cord from gum & hence adjusts C/A (Cross Axis) or R/S (Roll Straightening) and fills in the center with rubber at the expenses of the outer edge zones. The result is a final fabric profile with edges that have high EPI count and low rubber insulation and centers that are the reverse, i.e. low EPI and heavy rubber gauge. Yet the scanner profile will indicate all is well. Even though the scanner may indicate an overall profile that is within spec, the edges may be out of spec, with excessive cord EPI distribution, and low rubber insulation thickness, while the center is out of spec with low EPI and heavy rubber gauge.

Technology is available to solve this problem. The small size and high accuracy of modern on-calender gauges permits using 3 gauges on the top and bottom gum walls, 6 total, to assure a flat sheet. Visit the FACTS website and search out our ON-CAL3 gauging system.

Since both top and bottom gum walls are now precisely controlled and assured to be flat and on spec, the scanner will provide a more accurate representation of the profile. Heavy edges for example, would indicate cord distribution problems.

The stock temperatures, bank sizes, and work history all directly influence roll-separating forces. Minimizing variations in these 3 important process parameters will minimize variations in roll separating forces, and this in turn will minimize gauge variations. Good mill and bank control practice also results in improved uniformity for other final calendered gum and/or fabric properties.

The feed to the calender must also assure that the rubber bank does not have areas that stagnate. If rubber remains in the bank on the calender for an excessive amount of time it will partially cure and
become much harder. Edge trim that returns to the bank and stagnates is a common source of this problem. These areas will introduce gauge variations as well as negatively influence other properties of the calendered material. In extreme cases, burned lumps will appear in the calendered gum.

Regarding CORD PLACEMENT for corded rubber(tires):

Bands of hard stock also make it hard to properly penetrate the cord and may cause cord disturbance and improper cord distribution in these areas. In such cases the cushion force causes lateral movement in the nip and this results in cord displacement that is visible. Paired cords are often the first indicator. The thickness will be heavy and there will be cord displacement and irregularities but the weight of test samples will not be significantly affected.

These separating forces are large, as much as 160,000 to 300,000 lbs., at each actuator. The calender frame literally stretches from these forces. When the forces vary, the amount of stretch varies, resulting in the roll gap varying and this causes the gum wall gauge to vary.

From the previous post, it is obvious that speed changes should be avoided to the extent practical. A speed reduction from 50 ypm (yards per minute) to 10 ypm can result in a gauge decrease of 2 mils (.002”). Likewise a speed increase of 40 ypm from 10 or 20 ypm to 50 or 60 ypm can result in a gauge increase of 2 mils. Different calendars have different degrees of frame stiffness so the magnitude of the gauge change for a given speed change will vary accordingly.

The TCU (Temperature Control Unit) controls the temperature of the water exiting the calender not the roll surface temperature. This is an important distinction. When the calender is not actively processing rubber, i.e. during warm-up and when the calender is stopped, the roll surface is losing heat to the ambient and thus the TCU is actively heating the water loop. In this condition the roll surface temperature is between 10 degrees to 20 degrees F below the water temperature.

When the calender is running and actively processing rubber, heat is being generated so the TCU is actively cooling the water loop. In this condition the roll surface temperature is between 10 to 30 degrees F above the water temperature.

From this description it becomes apparent that for a constant water loop temperature, the roll surface temperature changes as much as 50 degrees F between the calender normal running condition and when the calender is stopped. This difference in roll surface temperature means that the rubber processed is being processed under substantially different conditions. Shrinkage and other properties will therefore be different.

To minimize the difference in processing conditions, the roll temperatures should be increased 30 degrees F whenever the calender stops. The temperature increase should be gradual and the specific amount should be experimentally determined by comparing roll surface temperatures in normal operation and after the calender has been stopped for 20 minutes. This function is available as a standard option as part of FACTS TCC 1600 calender control systems.