The Moriyama sheet preforming machine.

Since its inception, the dump extruder design commonly known as the sheeter has become synonymous with the name Moriyama, and with good reason. It was the Moriyama Manufacturing Works of Osaka, Japan that introduced this revolutionary design in the early 1980s to the rubber and plastics industry. Initially, the tire industry was the target market for this equipment. For years the tire companies had experimented with different ways of taking the batch discharge from an internal mixer and forming it into a slab to be effectively cooled and prepared for further processing, or additional mixing. Traditionally, the two roll mill was used to both improve the quality of the discharge batch and to remove the heat from the compound to prevent scorch. While effective, the use of mills is highly dependent on operator skills, and results are subject to variations in related conditions.

The roller type die extruder became more popular as improvements in raw materials, mixer technology and compounding processes resulted in greatly reduced mixing cycle times. The machine employs a feeder section in the form of one or more rams which force the batch material into a single screw extruder section which in turn conveys the material to a roller head section, which then sheets the extrudate. This equipment automates handling batch after discharge and eliminates the need for a highly skilled operator. However, there are drawbacks with the roller die extruders, most notably:

* contamination in the ram hopper and in the screw barrel and cylinder;

* increase in temperature of the stock passing through the machine due to pressurization; and

* relatively short useful life expectancy of the screw and barrel sections.

The concept for the sheet preforming machine, also known as the SPM, was developed in response to the shortcomings of the aforementioned equipment. The SPM concept is amazingly simple - drop the batch discharged from an internal mixer into a wide mouthed hopper which tapers to a casing featuring dual tapered screws, where the screws in turn convey stock material to a transition area. Here a bank of stock builds to a level where a sensor actuates the vertically oriented rollers to counter rotate and draw in the bank to begin the sheeting process. This article will address the SPM in terms of design review, features, options, ancillary equipment and various applications in which SPMs are employed.

Feeder section

The feeder section is essentially an open extruder consisting of twin conical intermeshing screws which begin large in diameter at the base and diminish in both shaft diameter and height of the screw flights to tips of the screws at the extruder mouth. These screws are driven by a single motor mounted on one extended shaft with the other shaft coupled through beveled connecting gears supported by spherical roller bearings. This assembly allows for use of the non-contact screw design. From base to tip, each screw tapers down in shaft diameter, flight height, pitch and flight tip-to-extruder casing clearance. The screw flights are engineered to ingest the batch and convey the material towards the transition area. The extruder is configured 15 degrees off the horizontal so as to achieve a downward angle for the flow of material.

The flights are manufactured of stainless steel and are hard chrome plated. The shafts are made of chrome moly steel and are often hard chrome plated as well. The material contact sufaces of the extruder casing are manufactured from stainless steel. All stainless steel surfaces are polished and buffed to a smooth mirror-like finish. The extruder casing and barrel, along with the screw shafts, are all jacketed for cooling.

Roller section

The extrudate from extruder/feeder section enters a transition area where a bank of material will build in preparation for sheeting. This area is enclosed on either side by adjustable stock guides, however, remains open at the top.

The bank height is measured by a bank displacement detector. When an adequate bank level is realized, the rolls begin to move and draw in the material from the bank to begin sheet production. Coordination of proper (predetermined) speeds for both screws and rolls will ensure stable sheet production.

The bank level detector interfaces with the extruder screws so that when the bank is low, the screws speed up, and when the bank is high, the screws slow down. The end result is to maintain continuous sheet production while maintaining the desired amount of compound in the bank area.

The roller section consists of two counter rotating, vertically positioned rolls oriented at a 90 degree or greater angle to the extruder section. The angle is determined by Moriyama based on production requirements, SPM size and user application. The rolls are made from chrome moly steel, and they are jacketed for effective cooling.

The roll nip is adjustable, typically from 0-10 mm to control sheet thickness. This can be done manually or (mechanically) by motorized means.

Digital indicators on each side of the roller section display nip settings, as detected by potentiometer, for accuracy in adjustment. Actual sheet thickness may vary, depending on roll speed and die swell characteristics of individual compounds.

The rolls are protected by shear disk cassette assemblies which prevent risk of damage from the passage of foreign objects such as belts, screws or the occasional tool that may find its way into the machine.

The bottom roll is fixed in position and the top roll is movable beyond the normal operating range to enable more complete access or safety and maintenance.

On smaller SPM models, all components are mounted on a common base.

Feature advantages

No ram or mechanical pusher is required. The feeder extruder is designed to accept the discharge batch as it is, the screws effectively draw in the batch and impel it forward along the inclined slope of the extruder casing.

Batch temperature reduction is realized. The action of the screw flights causes material to be ingested and turned over, thereby exposing more stock to the cooled metal surfaces of the machine. There is a large surface area in the open extruder relative to the working area about the screws. The heat sink is further enhanced by the non-contact screw design (insignificant work input to the material), the relatively slow rotation speed of the screws, and the open hopper structure. The overall effect is minimal energy input (low speed, minimal friction, etc.) and effective cooling for a net temperature reduction.

A blending effect is achieved through the intermeshing tapered screw design. The additional blending of the batch and material flow patterns allow for the batch to meld during transport to the roller section.

There is reduced risk of contamination. The open hopper and open transition (i.e., bank) area are relatively accessible and through the placement of angled mirrors and/or hopper access doors, visual checks are easily done. The extruder has proven to be remarkably self-cleaning, and there is typically no significant residual rubber requiring cleanout.

Automated operation of the SPM is made possible by synchronization between the bank level displacement detector and the extruder motor to provide continuous sheet production for a single batch or for a multi-batch production run. Furthermore, the SPM can be easily interfaced with upstream or downstream equipment to achieve a fully automated production line. Once pre-established process parameters are downloaded from a recipe, production can proceed without any operator intervention. Level sensors can also be provided in the hopper to synchronize with the roller section motor in order to coordinate batch evacuation from the SPM with the mixer batch cycle time. The less labor intensive operation reduces dependency on human intervention and its associated costs.

There are low maintenance needs for the SPM. The non-contact screw design, robust structure of the machine and slow rotation of screws and rolls minimize the wear and tear on the equipment. Operation of the SPM keeps downtime requirements to an absolute minimum.

Exposure and liability are limited due to low maintenance requirements and minimal operator presence.

Extended useful life is provided through a combination of non-contact design, robust structure and slow rotation speed for the screws and rolls. Hard surfacing materials protect compound material contact surfaces from wear and corrosion. Also, energy input is minimized, thereby reducing stress and strain transferred to the compound.

SPM applications

With more than 500 Moriyama SPMs having been manufactured, there are numerous applications for which the machine is used. As previously mentioned, there are many employed by the tire companies and these include many of the larger models produced.

Increasingly, this machine has gained favor with the non-tire or technical/mechanical goods manufacturers. These applications include belt, hose, wire and cable (sheathing and insulation), adhesives, golf ball, wall and floor tile, oil seal, printing rolls, weather stripping, rubber fabric coating, automobile floor mat and custom mixing applications.

Available options include specialized hard surfacing, different diameter rollers, hydraulically driven screws and rollers, motorized or hydraulically actuated stock guides, motorized or hydraulically actuated roll gap adjustments, infinitely variable level bank detection device, roller head angle and water-cooled stock guides.

Ancillary equipment includes a recommended four-zone TCU, one for screws, one for extruder casing/barrel and one for each roll. An edge trimming device is used for nearly perfect sheet edges. Slitters transform sheet/slab stock into strip form. Dancer rolls trim takeaway conveyor speed in sync with roll motor speed to reduce sheet tension.