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Batch processing improvement via retrofit.

When walking into a typical rubber mixing and millroom facility today, one would still see many of the elements that have made this the same, less than desirable working environment it was ten or twenty years ago. For many rubber processors the millroom batch off process, in particular, remains a dirty, unpleasant and labor-intensive process. Much of the machinery and equipment in these processing facilities is not up to technical standards seen in other manufacturing processes.

These rubber processors need to realize that batch off machine systems have indeed improved over this decade. Significant quality and productivity advantages can be realized by incorporating these machine improvements into their operation. Better slurry containment, automated strip making, noise control and improved automatic materials handling are a few examples. These companies also need to realize that these features can, in many cases, be incorporated without having to replace entire millroom facilities. This is accomplished through the use of modular retrofits. The purpose of this article is to present the less costly alternative to a complete batch off replacement. Batch off retrofits are a low cost investment alternative to provide high process performance.

Batch off lines offered by principal machine suppliers are designed and built primarily in modular form. Individual components can be added or replaced in existing machine lines to boost process performance. Components such as hinged inlet conveyors, impression markers, splice presses, slitters, dip tanks, reservoirs, mix tanks, blow-off knives, festoon cooling sections, chillers, pick-offs, cut-off knives, straight line stackers, strip stackers, automated skid handling, access platforms and controls are all available as batch off retrofits.

Over the past several years, significant technical strides have been made on the technical front in the area of batch off processing equipment. No longer is it required to accept rubber processes that are plagued with inconsistent coating and cooling of stock. No longer does stock coating and cooling need to be a highly manual operation with extensive relocation and handling of material to perform required secondary tasks.

Today's batch processing equipment boasts high levels of automation through the use of PLCs and other devices such as automatic stock marking, stock sampling, cut-offs and weight measurement. New equipment designs have produced machinery that can be expected to deliver higher service reliability while incorporating a myriad of former off line activities as primary functions such as strip, slab and sheet processing. New control designs allow maximum flexibility while providing diagnostics and maintenance information.

The changing face of the rubber processing industry has forced many companies to broaden their product lines to include compounds of various durometers and green strengths, as well as other material properties too numerous to mention. Tighter quality requirements by way of the ISO and QS-9000 specifications are required by many of today's end users. Not only are consistent coating, cooling and dryness of stock important issues to address, but other issues, such as stack appearance, are now also of paramount importance.

Competition in the rubber processing field is fierce. Increases in efficiency and minimization of downtime are essential ingredients in the race to remain competitive. High utilization rates require mixer upgrades for faster material throughput. As a result, downstream processing equipment must be ready to handle these special processing demands in a reliable, cost effective and efficient manner that will produce a quality product in the shortest possible time frame.

Several alternatives exist to achieve these goals for batch processing improvement and flexibility. One answer may be to completely replace an older batch processing system with an entirely new system. This method is generally considered viable for some lines. However, obstacles such as facility size constraint and the lack of modularity of some systems required for this higher capacity batch processing must be carefully considered.

A second answer may be to provide additional off line processing equipment. Newly developed technology provides for stand alone equipment designs that specialize in the handling and packaging of special materials such as strip stock. This stand-alone equipment is often easily added to existing batch processing lines to provide increased product handling capability and flexibility.

Thirdly, when processing capabilities are overmatched by certain material requirements, outsourcing of selected materials may be a reasonable, if not desired, solution.

A fourth answer for achieving new processing goals may be retrofitting new specialized equipment to existing batch processing systems. This is often the most cost-effective solution to achieving new processing goals. Implementation of retrofit components can provide a wide range of possible improvements including additional cooling capacity, better slurry coating, better automation of handling and better stacking of milled or extruded rubber product resulting in high accuracy laydown for ease of transportation. Another benefit of retrofit programs is that installation and implementation of the retrofit machinery components can be achieved in a time, frame that is significantly less than a complete system replacement would allow. Lower costs can be realized utilizing existing components instead of replacing an entire system.

Strip handling

Increased need for and therefore increased production of strips is a problem of older batch off machinery designed and built for slab handling. Several retrofit components are available to improve the continuity of coating, increase cooling capacity and automatically handle strips.

Adjustable mill knives

The knife assembly is designed for cutting rubber sheet stock off of a two-roll mill. The device is mounted to the end of the hinged take-away conveyor. The knives are automatically or manually adjustable for different stock widths. There are two non-rotating circular knives that contact the mill roll, which are designed to prevent mill roll damage.

Notched knife slitter with notched knives

The slitting unit is designed for cutting the rubber slab into continuous strips with perforation attachments between each strip. Circular slitter knives (with notches) are independently mounted to air cylinders and are mechanically adjustable. Each knife can also be individually selected to be raised or lowered. To facilitate adjustments, an access platform can be provided as an option on the operator side of the machine.

Description

For example, a notched knife slitter can be designed to create rubber strip stock from continuous sheets, or milled or extruded rubber stock. The slitters under this specification can be integrated directly into a batch off system, but can also be retrofitted to other systems. The rubber strips are made using a series of notched circular disc knives that can be individually set to obtain a choice of number and width of strips. The strips are connected only by notches, keeping the sheet intact for easy handling during the coating, cooling and stacking process.

Features

This slitter offers the following advantages:

* The number of strips and width of strips can be easily changed from batch to batch. Individual knives can be raised out of position if desired while width changes require a simple mechanical adjustment.

* The number and size of the notches are set by the notch cut into the circular knives.

* The number and size of the notches is easily adjustable.

* The blades are individually replaceable without the need to re-sharpen all knives.

* Each knife is individually controlled to allow maximum flexibility.

Accurate strip stacker

Strip stackers are devices designed to receive narrow rubber strip and deposit it neatly onto an open pallet. A three-axis stacker allows for accurate positioning of the driven pinch rolls which controls the strip at all times. Bi-directional material laydown combined with moving hold down flaps provide stable, dense material stacking. The ability to control the strip will create a uniform stable freestanding stack of rubber. Stackers can also rotate the skid 90 [degrees] to create an interlacing of rubber strips with one double layer over the previous double layer. This automated machine requires operator assistance only for starting and stopping operations of each pallet stack. Speed matching between the strip supplying device and the stacker is accomplished by the use of a free loop and controls. The free loop acts as a buffer to allow accurate speed control.

Coating and cooling strip handling

Older batch off equipment is notorious for inconsistent coating and for lack of control of the slurry. Housekeeping problems were accepted as a necessary part of slurry handling. Design improvements to both areas are available for retrofit to older machines.

Dip tank unit

The dip tank is of non-corrosive construction and is located between the inlet (take-away) conveyor and the festoon entrance. The unit is designed to take warm rubber from the inlet conveyor and pass it through an anti-tack solution. The dip tank works in conjunction with a reservoir to circulate and agitate this slurry solution.

The slurry is pumped up from the reservoir and flooded through the shallow dip tank. The warm rubber is carried through the tank using a special stainless steel wire mesh belt and dip roller assembly that guarantees coating of the rubber, minimizes deposits and prevents jam-ups. The slurry overflow falls back into the reservoir through a stainless steel filter. The filter prohibits rubber crumbs or other foreign materials from entering the slurry solution.

The unique design of the slurry handling system allows for a constant circulation and smooth flow and thorough coating of rubber stock. When placed as part of a machine order, the dip tank includes the reservoir and blow-off options. Options such as level controls, standby pumps, etc., are also available.

Reservoir assembly

The corrosion resistant reservoir is designed as a holding tank for the anti-tack solution. The tank is furnished with a circulation pump which pumps a percentage of solution to the dip tank and the remaining capacity is circulated back to the reservoir to agitate the slurry solution. The pump and reservoir are mounted on a one-piece steel skid-like frame for easy removal.

Reservoir agitator

The reservoir mixer/agitator is used for additional mixing in the reservoir tank. The mixer/agitator consists of a motor, drive shaft and prop. The mixer can be set up to continue mixing even when power is removed from the batch-off machine.

Blow-off knife

The blow-off knife is mounted at the exit of the dip tank. The blow-off knife is designed to reduce the amount of slurry or anti-tack carried over into the festoon. The blow-off knife consists of an electric motor, blower assembly and adjustable air knife.

The air knife is mounted such that the angle is adjustable in relationship to the stock. The knife opening is also adjustable to allow the proper amount of air pressure to be applied to the stock for optimum drying.

Automated high accuracy stacking packages

Improvements in stacking, palletizing and handling facilitate in-plant and interplant transportation and provide better aesthetics in packaging.

Automatic stock pick-off

This device is used in a festoon batch-off system to automatically transfer the beginning of the rubber sheet stock from the festoon cooling rack to a pullout conveyor.

It consists of a controlled gripper arm, lifting arm and shifting mechanism. After a photocell senses the stock, the first loop of the sheet is grabbed off the festoon bar. The gripper is designed to reliably hold and pick up a single sheet without distorting the stock. After gripping the stock across its entire width, the assembly is shifted toward the pullout conveyor and drops the leading edge of the stock on the conveyor in front of the pinch roll.

Draw knife cut-off

The draw knife cutter is designed to reliably and economically cut off continuous ribbons of stock after the desired payout is reached. The multiple blade cutting head is drawn across the strip while pneumatic cylinders clamp it into position, thus providing a clean separation of material. Accuracy of clamping and cutting are guaranteed by the use of linear guide rods. The knife is designed for use with single slab thickness.

When the cutter is in the open position it provides a 6" opening, reducing the chance of jam-ups.

Straight line wig wag stacker and lift

These high accuracy stacking packages offer flexibility in handling continuous milled or extruded rubber sheet stock. It is designed to accurately stack onto pallets continuous sheets of stock in a wigwag fashion up to five feet high. This machine can be retrofitted to most batch off systems and works best with an automatic pick-off and indexing pallet conveyor, providing total automation to the final batch off process.

This stacker is at the end of the batch off system and accepts stock from the cooling rack drive section manually or with an automatic pick-off. The module consists of a structural steel frame, a wigwag pendulum basket driven by a variable speed AC motor, two independent press-down devices and a hydraulic lift platform. This combination accurately stacks the stock onto the pallet where the stock press-down devices fold the wigwagged ends to create a neat looking stack. The variable speed drive of the pendulum basket and the close proximity of the laydown surface allow for a variety of skid sizes to be used with equal laydown accuracy.

When the proper stack height is reached, stacking movement is stopped, stock is cut (if so equipped), and the lifting platform lowers to the floor.

The machinery is equipped with necessary safety guards and E-stops. It will operate at speeds up to 130 ft./min. Under normal conditions, the stack width will not vary from center-line by more than [+ or -] 1-1/4" from side to side and [+ or -] 2" on overall length using standard tire stock. The rubber should be soft, pliable, uniform and have the green strength to allow a pick-off from the festoon. The stock must be of a consistent width, thickness, and not have holes that allow the stock to stretch. Stock stretch and shrinkage must be even from side to side. The stacker will not improve the accuracy of the material provided to it.

Pallet weigh scale

The pallet weigh scale is used to determine the total weight of the rubber on the lift platform. The weigh scale can be `tarred' to zero the weight after the skid or pallet is placed on the scale. Depending upon the option selected, the scale can be used to: display the current weight; allow a set point and provide feedback to the PLC when that point has been reached; display the current weight and provide feedback to the PLC. Other options are available. The basic unit includes a batch type controller.

A platform scale is usually mounted on a lift platform and is a flat top scale. The pallet sits on top of the lift.

Scissors lift with hydraulic unit

The scissors lift with hydraulic unit is designed to lift the material pallet to a constant height under the let-off unit to improve stacking accuracy. The lift is raised hydraulically to the optimum height and slowly lowered to maintain the distance to the wigwag unit as stock is placed on the pallet. An electrical sensor is used to determine this height.

Pallet conveyor

The pallet conveyor unit is designed to automatically shift empty or full pallets of wig wagged rubber from the empty skid position to the load position and then to the full or unload position at the stacking end of the batch off machine. The pallet conveyor is capable of handling a variety of skid and basket configurations and can be mounted flush with the floor or raised above the floor. It can be designed to allow the use of skid lifts and weigh scales.

This unit is designed to have positions for empty skid(s), one is for the skid at the wigwag, and additional position(s) for full skid(s).

When the skid conveyor is purchased with a batch off having a high accuracy stacker, a lift unit is furnished. When a preset stacking height is reached, the lifting unit will lower automatically; the full skid moves away and an empty skid is moved to the stacking position and is then lifted for the start of another stacking cycle.

Storage magazine for skids

This skid handling system is designed to handle metal skids. It is located at the end of the skid conveyor. The main purpose of this unit is to store empty skids and dispense them as needed to the skid conveyor. As designed, the magazine is completely automatic and pneumatically controlled by photo eyes. The tow motor driver supplies the first skid position with a stack of empty skids; the magazine moves forward to surround the skids and picks up the stack, leaving only the lower most skid to move into position via the skid conveyor. As the conveyor is indexed, the magazine dispenses an additional empty skid until the magazine is completely exhausted, requiring refilling.

Additional available retrofit components

Many other components are available for retrofit to improve the batch off performance.

Cooling rack extensions with bars and fans

The cooling rack extension section consists of a structural steel frame connected to the festoon entrance and cooling rack drive to form a complete, sturdy, compact unit. The ventilators are situated in such a way that the airflow passes over the rubber and is diverted by means of deflector plates to prevent excessive airflow at the operator's level. The cooling rack extension section also includes a walking grid along tire bottom for maintenance and cleaning of the machine.

Festoon cooling fans

The low noise cooling fans, located along the festoon, are designed for the cooling and drying of the rubber stock as it passes along in the festoon. The fans are situated in an over and under arrangement to allow for full cooling of all length festoon loops. The fans consist of an electrical motor, fan blade, housing and finger grills. The low noise cooling fans are designed such that, when incorporated into a festoon section, the accumulative noise generated is less than 78 Dba.

Chilled air systems

This system is designed specifically for use with the batch off system and is located along the sides of the cooling festoon. The purpose of the chilled air system is to assure lower lay down temperatures of critical compounds. The system includes cold water to air radiator, fan, in-line filter and controls. Optionally available is a refrigeration unit and galvanized ductwork.

Pull-out conveyor

The conveyor is designed to pull rubber from the cooling rack and deliver it to the wigwag unit. An AC gear motor drives the conveyor belt. A pinch roll is included at the conveyor entrance to capture and sense the stock. Pull-out conveyors are available in a wide variety of configurations.

Electrical controls

All retrofits are available with full controls. The machine is supplied completely wired and provided with all operating and control equipment for the above mentioned elements. The PLC controls all machine functions. The main disconnect switch is mounted in the control cabinet containing all the electrical components. Furthermore, there are push button stations located near the mill operator and the discharge stacking area. The installation includes safeties to ensure a justified and safe functioning.

Retrofit controls are also available to allow for the current needs of the rubber processing facility. Data tracking and processing are achieved with the use of the new PLC designs.

Man machine interface and full diagnostic packages improve machine uptime. Communications to other machines or overhead systems are standard.

Selection of a supplier to provide batch processing retrofit components or systems should be based on the supplier's approach to system design. Modularity of design, as well as proven performance and flexibility, are critical areas to investigate. The use of new technology as a basis for design is essential in producing a process solution that is not obsolete before it ever sees the production floor. Compatibility of component design to accommodate ease of installation into existing systems is also a desirable feature when dealing with retrofit requirements. The tie in to existing controls or replacement of the existing controls is critical to the success of any retrofit.

Additional consideration needs to be given to design alternatives that provide functionality. This fact is especially true when dealing with retrofit projects. The ability of the supplier to provide a module style that suits the process requirement exactly will result in a superior end result. Variations in dip tank style, cooling methods, level of automation, stock transfer systems, strip, slab or sheet handling, and other component configurations, all contribute to a supplier's ability to provide results that are in precise accordance with the processors' demands without shortcuts.

The ultimate goal of any performance enhancing expenditure is to improve process return on investment. In this respect, selection of the correct machinery or retrofit package should carefully consider machinery investment versus expense, components that will lower total process cost, the amount of automation that will be required for efficient operation, and service through the useful life of the equipment. Selection of a supplier whose expertise from both a process solution aspect and a budgetary view, based on customer requirements, will go a long way toward the success of any machinery upgrade program. Be sure that a would-be supplier of such equipment can readily meet all of these needs.

Recommendation of the components to meet the criteria previously stated in this presentation can only be achieved through a thorough understanding of a given process. This process knowledge must be gained by identification and measurement of cost variables, along with determination of both process tolerances and specifications. Superior machinery component and retrofit suppliers will offer programs such as one day on site surveys to gather such important information. During these surveys, not only can process parameters be defined, but the ability to physically view a plant area can provide invaluable information that will impact any required design alternatives.

Be sure that the supplier you choose is capable of providing all of the services that have been outlined, as well as a broad range of tested and reliable machinery for process solutions. A small amount of research can yield tremendous success.

In conclusion, batch off retrofits are available as a low investment alternative to help achieve high process performance. Retrofit improvements to cooling, coating and stacking are available, and machine automation allows for lower labor costs. New control systems are available to improve machine uptime, but also to implement compliance with quality control.

It is my recommendation that rubber processing facilities consider batch off retrofits as a measure to improve the millroom products. Improvements that are needed in coating, cooling, stacking and automation are available at low costs and provide the high performance needed to compete in a highly competitive market.

(This article is based on a paper given at the September, 1999 meeting of the Rubber Division.)
COPYRIGHT 2000 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2000, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
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Author:Rastok, Phillip A.
Publication:Rubber World
Geographic Code:1USA
Date:Jul 1, 2000
Words:3746
Previous Article:Continuous, non-contact splice width measurement for calendered products.
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