Accessory equipment for tire manufacturing.

Accessory equipment for tire manufacturing

The manufacture of tires has been likened to the ancient art of making pottery. First, you mix the clay (internal mixer), apply the clay and shape it to the potter's wheel (tire building machine) and finally bake it in an oven (curing press).

That's the basic process. Simple. Nothing new under the sun. If that's the case, where did all those patents come from? Of course the process of making a tire is much more complicated. Before the end steps of tire building and curing can be reached, many intermediate steps are required, each involving specialized machinery to make those steps economically possible.

The machinery for these intermediate steps are what we call "accessory equipment for the manufacture of tires."

In the early years of tire manufacturing, the major tire companies designed and built almost all of their own machinery, including curing presses and especially the tire building machine. (Tire companies seem to have a special affection for their potter's wheel). Even today, the large tire companies design and manufacture (or have manufactured by others), a large part of their equipment, but in recent years, as the competitive business climate caused downsizing of their in-house staff, the amount of in-house-designed equipment has declined, leaving room for small engineering-oriented firms to help fill the gap.

Accessory equipment as relative to the manufacture of tires, usually involves one or more of the following activities:

* material handling;

* stock preparation;

* pre-assembly of components;

* weighing, measuring;

* production testing, grading.

Material handling

This is a broad field of endeavor, and of course relates to nearly every activity concerning manufacturing of all kinds. In the case of tire manufacture, this subject involves handling the raw materials including incoming gum, chemicals, fabrics, steel cord; movement of in-process components, and semi-finished product; the changing of tire molds; movement of finished product, and storage, packing and shipping. Steel cord handling and creel loading, steel cord organizing and payout of cord to the calendar under constant tension are primary processes in tire building.

Steel cord usually arrives at the tire factory in standardized cartons, or in some cases, barrels, from the steel cord manufacturer.

The steel cord is typically wound on semi-standardized metal (sometimes plastic) spools with a filled weight of either 40 lbs. each, or 80 lbs. each. Within this basic selection of the two principal sizes, there is a further choice involving the bore size of the spool, and the drive-pin diameter and offset distance.

Within the constraints of availability, selection of spool size (weight), spool bore size, and drive-pin arrangement are usually made by the end user.

There have been many approaches to spool handling, such as special fixturing to enable loading of a multiplicity of spools onto the creel spindle. Usually this approach results in double handling, since the fixture itself requires loading, resulting in a total loading time in excess of that deemed desirable.

We have favored the direct approach to loading. That is, the cartons of spools are delivered to an appropriate location on the creel room floor, and the creel loading machine works directly from the spool carton to each spindle of the creel. Figure 1 illustrates typical direct creel loading.

The success of the creel loading machine is largely dependent upon the means of grasping the spool. The spool must be grasped in such a manner that the steel cord is not damaged, and such that either end of the spool may be selectively loaded onto the spindle. The latter requirement prevails because most creels have tension controllers and spindles on both sides of the creel framework, and the steel cord is unwound (when payed-out) through the tension/organizing rollers in both right-hand and left-hand configurations.

Overriding all of this is the safety aspect of creel loading. Spools of steel cord weighing 80 lbs. or even 40 lbs. are potentially hazardous when lifted from the carton to the spindle. The grasping device should therefore be as safe as possible, or "fail-safe." Of course, nothing is 100% fail-safe, but the grasper is designed to retain its grip in event of power or air pressure failure. The grasping device can be offered in a single-spool, two-spool, or three-spool configuration, and with the option of air-pressure or manual actuation. The selection of the grasping device would largely depend upon the type of loading machine to be used, and upon the economics of the particular factory involved.

For creel loading, three basic types of loading systems are recommended:

* Simple hoist, using a single-spool manually actuated grasping device, with optional overhead support structure. This system is mainly used where production is low, or where labor is plentiful and cheap.

* A microprocessor-controlled loading machine. This machine is usually equipped with a two-spool air pressure actuated grasping device, and is controlled in its movement by the programming of an internal computer. The machine moves under program from spool carton to the appropriate spindle, and back to the next two spools. The operator does not have to hunt and seek his position. The grasping device opens, closes, rotates 45 [degrees] to enter the carton, and the pair of graspers spreads from a 10 inch center distance reflecting the spacing of the spools in the carton to the wider spacing of the creel spindles, typically 12 inches, all done under program automatically.

The end-for-end selection, that is, deciding which end of the spool is entered onto the spindle, remains an operator selection and is performed manually. There are various creel loading machines offered depending on speed and price.

* An air-balance creel loading machine is one of the latest additions to the creel room. This machine is of modest price and is affordable to the end-user engaged in an intermediate level of production. It has been designed for a creel room of low head room, and in many cases, suitable for retrofitting to an existing creel room.

Employing an air-balance hoist and an air-pressure actuated single-spool grasping device, these machines take much of the manual effort out of the creel loading process. Its operation is designed to be simple, employing only two push buttons: unloaded pressure and lifting pressure. Closing and opening of the grasping device is inter-connected with the lifting pressure and unloaded pressure. The lifting pressure is set to offset most but not all of the weight of the grasper and full spool. The operator supplies a few lbs. of force to lift the spool to the spindle. After delivering the spool to the spindle, and switching to unloaded pressure, the loader remains in suspension until the operator moves it with a few pounds of force to the next spool in the carton.

Safety devices have been installed into these machines to prevent sudden fall upon loss of air pressure, or sudden rise in event of sudden increase of pressure when the spool is in the unloaded condition. A spool sensing device is employed to make sure the grasper is in position before activation of the lifting pressure.

After filling the creel with the required number of spools, the creel must be threaded through the organizing system to the calendar. This remains a manual operation and its mechanization awaits solution by some enterprising engineering company. But for the time being, it is manual.

Once the task of creel threading is completed, the calendar run may be started. The creel system has the task of paying out the cord smoothly with a substantially uniform tension during the creel run, and must operate over years of use under the conditions of a dry, warm atmosphere. To do this, tension controllers are offered with air-pressure operation. Tension is created by use of a brake shoe engaging a precision brake drum. The cord tension is adjustable by use of a low internal friction rolling diaphragm air cylinder. Tension is changed over the whole creel by adjusting only one air-pressure regulator. All tension controllers deliver the same tension because of its inherent design, that of a force-balance device.

Stock preparation

Preparing the material stock for incorporation into a tire includes (in the case of textile materials) dipping, heating, stretching, drying and calendering (although these tasks are often treated as a separate activity owing to the importance of each in a tire factory), sheet gum preparation, slitting and bias cutting.

In the realm of stock preparation, this article will deal with slitting. Slit material of many types are required in the tire. These would include:

* calendered fabric chafer stock. (Chafer is usually square woven calendered rubberized stock applied to the bead area to absorb tire rim chafing of the bead);

* bead cover stock;

* flipper stock;

* gum strips of many widths (The term "gum" is often used to refer to an uncured rubber compound, which in this case, has been calendered to sheet form)

Calendered stock, either rubberized textile cloth or plain gum is usually delivered to the slitting line, and when needed, loaded into the stock let-off, which is the first step of the slitting process. The stock let-off must be prepared to handle stock rolled up in a liner, which may be of cloth, or plastic sheet, often vinyl. From the let-off, the material is guided to the slitter for slitting to the desired width.

The slitter contains multiple slitting rotary knives, which are adjustable laterally for various cutting widths, and is provided with adjustable down-pressure for cutting various thicknesses and material types.

At the down-stream end of the slitter line, the stock must be wound-up, usually in some type of liner, for later delivery to the next step in the manufacture of the tire.

Preassembly of components

Components are preassembled in cases where it may be impossible to accomplish the task otherwise, or in cases where it is more economical than assembly at the tire building machine. Then, too, most tire factories do not like to have their tire building machines tied-up doing tasks that may be done quickly on less expensive machinery.

Typical of preassembly tasks are assembly of tire body or carcass plies, breaker plies, application of apex (a filler which fairs the body plies to the bead), application of flipper stock (a reinforcement tying the bead to the tire body plies) and application of bead cover stock (either gum or rubberized fabric) to the bead.

The pre-assembly of body and breaker plies is one of those tasks that can be done at the tire building machine, or can be performed on a specialized machine prior to delivery to the tire building machine. Such machines are known as band building machines or sometimes as pocket building machines. At one time, a large percentage of the tires made were manufactured using the band building method, including passenger car tires, truck/bus, airplane, agricultural and earthmover tires.

Today, the process is employed mainly in the manufacture of airplane, agricultural and earthmover tires, although breaker plies are often made on machines for producing very specific sizes, for passenger car or truck/bus tires.

Since the tire band building process is mainly confined to large, low-quantity tires, the band building machine preferably should offer the capability of rapid size-changing, and many features such as ability to apply gum sheet to the plies as they are built.

Usually band building machines range in band width of 48 inch to 200 inch, each size of which also has a variety of circumferential ranges which are selected by the end user.

On the other hand, bead covering is one of those tasks which must be done prior to the installation of the bead into the tire carcass. No tire manufacturing factory likes the job of bead covering. To the production people, covering beads is a nuisance which they'd like to avoid. Indeed, in many factories, beads are no longer covered. But a bead cover is required in many tire specifications, so it is still necessary to provide equipment for this task.

From the machine manufacturer's standpoint, a bead covering machine is difficult to standardize because each customer has his own requirements, including variations in the material to be applied to the bead. This means that some tailoring of the machine is required for each customer.

The envelope cover, which is a strip of rubberized calendered fabric, is applied longitudinally around the bead, and encases the cross-section. In some factories the beads are covered completely, while in others only the start and finish areas of a wound bead are covered.

The spiral bead cover is just as is described - rubberized fabric tape wound spirally along the circumference of the bead. Envelope covering is much faster than spiral covering. To fully cover a 15 inch diameter passenger car tire bead may consume 2.5 seconds, whereas the same bead spirally covered may consume 20 seconds or more. Because of the large difference in labor cost, spiral covering is seldom used on passenger car tires, but will be found on aircraft tires, heavy duty tires and earthmover tires.

Weighing and measuring

The ingredients of the tire, as with any precision product, must be uniform from piece to piece. To accomplish this, considerable use of automatic batch weighing devices is made, especially at the mixing of the raw materials with the required chemicals to produce the rubber compounds from which the tire is manufactured. In-process continuous weighing is also employed, principally at the extruder lines producing tire treads and sidewalls, to maintain the uniformity of these components.

Continuous measurement and control of thickness of rubberized textile or steel cord sheet delivered by the calender line has enabled the tire maker to maintain thickness uniformity across the width of the calendered sheet, resulting in cost saving of material.

These weighing and measuring requirements have been filled by specialists supplying accessory devices, and the efforts of these specialists have contributed greatly to the uniformity and cost containment of the modern tire.

Production testing, grading

Specifications may be mandated by government; by the tire customer (usually an automobile manufacturer, but may be a tire marketing/distributing company); or may be required by the in-house specifications of the tire manufacturer.

The term production testing is used here in the sense that the product itself is substantially finished, and undergoes testing to confirm the conformance of the product to the required specifications of the completed tire, as opposed to in-process testing of materials and dimensions of components. Production testing would include:

* endurance/high speed wheel test;

* plunger and bead unseating test;

* uniformity grading.

There is machinery for conducting the government-mandated test of tire carcass strength and bead unseating, as described in the Federal Motor Vehicle Safety Standard No. 109. In the destructive test of tire strength, a specified steel probe is pressed into the central part of the tire outside diameter at a specified speed until rupture occurs. The load and depth of the steel probe at rupture are noted, and computations according to the Standard are made. Comparisons with the acceptable minimum values determine whether or not the tire conforms to the Standard.

The bead unseating test is used to measure the load required to force a tubeless passenger car tire off a rim under certain conditions of test, as specified by Federal Motor Vehicle Safety Standard 109.

In this test, the tire is mounted and inflated on a production wheel or rim. A bead unseating block of defined configuration is brought to bear against the sidewall of the tire until the seal of the tire to the rim is broken and air pressure collapses. The peak load to accomplish this is recorded.

The future of accessory machinery

Even though the manufacture of tires has been likened to making pottery, new and improved equipment will always be needed. Changes in design and process are not made in haste. A tire maker going to a tire factory of 50 years ago would not feel uncomfortable; he would recognize much of the same equipment that is presently in use.

Nevertheless, the tire maker is always on the lookout to make improvements in his product, or for cost reduction; that's the tire maker's lot; he's stuck in a very competitive mature industry. He must make the incremental improvements and cost savings in his product. Then too, there's the government bureaucrat that's looking for a way to keep himself in his high pay, no-work job by imposing requirements on the tire maker that may or may not be worth the cost. But out of all this comes opportunity for the accessory equipment manufacturer.

PHOTO : Figure 1 - typical direct creel loading