Glass Packaging Institute

Section 3.1: Glass Making Overview

Fri, 19 Dec 2008 16:42:22 -0500

Creating glass containers is a capital intensive, 24 hour, seven days-a-week, 365 days-a-year, manufacturing process.
Container shapes are made through the controlled shaping and cooling of molten glass into a desired form.
State of the art equipment is used throughout the process to produce large quantities of glass containers in a relatively short period of time.
There may be as many as eight forehearths and machines per furnace. Large machines are capable of producing more than 700 bottles a minute that are far lighter in weight than ever before.

The Production Cycle

Link to online map

Click on the image to the right for an online interactive map of a glass container manufacturing facility.

continue to Section 3.2: Batch House

Section 3.2: Batch House

Fri, 19 Dec 2008 16:37:47 -0500

Raw materials arrive at a glass plant batch house by rail or truck and are visually inspected and sampled to make sure they are a standard size.
Materials are discharged into an unloading pit, sent by elevator transport to the batch house, and then to the proper storage silo.
Before going into the furnace, materials are proportioned into batches and weighed on scales located under the storage silos.
There is usually one scale for each raw material and each batch must be accurate.
The sensitivity of the scales is monitored daily and their calibration is checked weekly to ensure accuracy.
Once weighed, materials are sent to the mixer, located just above the furnace.
In some plants cullet is added after the materials are mixed to minimize wear and tear on the mixer to allow for greater amounts of cullet.
The mixed batch is then transported to the furnace by a horizontal belt conveyor or monorail train.
Water is often added to the mixer just before the batch is charged into the furnace to decrease the possibility of dusting and segregation and inhibit de-mixing during transport.
A wet batch enhances batch pattern control in the furnace, which is important for efficient melting.

continure to Section 3.3: Furnace Operations

Section 3.3: Furnace Operations

Fri, 19 Dec 2008 16:36:33 -0500

After leaving the batch house, the mix is fed continuously into the furnace or tank where it is melted into glass.

The batch is charged into the furnace at the same rate as glass is being pulled out so that the amount of glass in the furnace is kept constant at all times.
Glass depth must be controlled to within ±0.01 inch for proper forming machine operation.
Furnaces consist of three main parts:

1. Melter
2. Refiner
3. Regenerators or Checkers

Most furnaces are designed to use natural gas but are capable of using alternate fuels-oil, propane and electricity-if necessary.
Furnaces range in size from about 450 to more than 1,400 square feet of melter surface.
Glass depth is between 4 to 5 feet.

A properly operated and well-maintained furnace will last for 10 years or more with just one partial repair and will produce over 1,000 tons of glass per each square foot of melter surface over the life of the furnace.
Energy use is about 4 million BTU per ton of glass.
Both furnace life and energy use have dramatically improved over the past 20 years.
Computers have the ability to tie together furnace, refiner and forehearth operations as never before.
Statistical process control techniques have also revolutionized furnace operations, leading to improved efficiency and glass container manufacturing quality.
Among the more recent developments is the use of oxygen boosting or oxy-fuel melting.
With oxygen boosting, oxygen and gas are injected into the combustion air to improve flame control and allow higher pull rates or lower temperatures.

With oxy-fuel firing, oxygen replaces all of the combustion air, eliminating the need for regenerators and combustion air fans. With this technique, manufacturers are better able to melt the glass and deliver it to the forehearth.

sideview.mpgTopView.mpg

Melter and Regenerator

The melter is a rectangular basin in which the actual melting and fining (seed removal) takes place.
In a side-fired furnace, the batch is charged into the furnace through the doghouse, which is an extension of the melter, protruding from the back wall.
Along each side of the melter, above glass level, are three to seven ports, which contain the natural gas burners and direct the combustion air and exhaust gases.
An end-fired furnace differs from the side-fired machine insofar as the doghouses are along the side and the firing is done through a single port and exhausting is done through an adjacent port on the end of the furnace.
The furnace is fired alternately in one direction and then in the other in 15- to 30- minute intervals.
The ports on the firing side direct the combustion air from the regenerators on that side into the melter.
The exhaust gases exit through the opposite ports and pass down through the regenerators on the opposite side.
Since the exhaust gases are hot, they heat the brick stacked in a checkerboard pattern in the regenerator.
When firing is reversed, the combustion air passes up through the hot bricks and is preheated, thus recovering energy that would otherwise go out the exhaust stack.
The melter basin is separated from the refiner by the bridge wall (throat end wall). Glass passes from the melter to the refiner through the throat, which is a water-cooled tunnel that extends through the bridge wall.

Refiner

In the past, the refiner was the region in which fining was accomplished, but with the higher pull rates in recent years, the glass must now be seed free by the time it leaves the melter.
The refiner now acts as a holding basin where the glass is allowed to cool to a uniform temperature before entering the forehearths.
The melter and refiner are covered by crowns to contain the heat.
The throughput load or pull on a furnace is commonly expressed as square feet of melter surface area per ton of glass pulled in 24 hours. This allows furnaces of different sizes to be compared on an equal basis.
Most flint furnaces are designed to pull at a rate of 3 to 3.5 square feet per ton of melter surface area depending on the type of glassware being made and the machine speed.

Forehearth

In the forehearth, heat from natural gas burners and cool fan air are carefully applied to the surface of the flowing hot glass.
Constructed as a long ceramic "bathtub" glass temperature is reduced as hot glass flows through the forehearth.
Glass is cooled from 2350 degrees F° at the entrance to 2150 degrees F° at the exit.

continue to Section 3.4: Forming Process

Section 3.4: Forming Process

Fri, 19 Dec 2008 16:32:29 -0500

Viscosity

Viscosity, a measure of liquid fluidity, varies inversely with temperature. As the temperature decreases, viscosity increases. As glass cools, it gets "stiffer" or more viscous.

Viscosity is measured in poise at a specific temperature. Molten glass in the forehearth at 2,200 degrees F has a viscosity of about 1,000 poise. As a point of comparison, consider the following examples:

Water at 70 degrees F has 1/100 poise
Light oil at 70 degrees F has 1 poise
Heavy oil at 70 degrees F has 7 poise
Honey or syrup at room temperature is 100 poise
Molasses in January (32 degrees F) is 10,000 poise
Asphalt is from 1,000,000 to 1,000,000,000 poise depending on the temperature

Gob Formation and Shapes

A gob is a specific amount of molten glass, which is eventually formed into a glass container.
The shape of the gob is important because it affects the way it enters into the Individual Section Machine.
There is an optimum gob shape for each glass container produced.
Gob length and diameter are dependent on the shape and weight of the container.

Consider these facts about the size, weight and heat content of a gob during formation:
Gob weights vary from ½ oz. to 48 oz.

Gob lengths typically range from ½ inch to 6 inches.

Gob diameter can be from 3/8 of an inch to 4 inches.

A 7 oz. gob is typical for a 12 oz. beer bottle.

At a temperature of 2,100 degrees F, the viscosity of a gob has the consistency of thick honey and it is uniform throughout.

A typical 7 oz. gob contains 275 BTUs; 40 gobs contain the same amount of heat as a small kerosene heater puts out in 1 hour.

An I.S. Machine can produce up to 700 bottles per minute.

Feeder and Delivery

Molten glass flows with the help of gravity from the refiner through the forehearth. From there it is carefully cooled to a uniform temperature and viscosity prior to reaching the feeder. Using the pull of gravity, the hot glass flows through the orifice at the bottom of the feeder. Glass flow is controlled by the height of a ceramic tube in the feeder; a raised tube creates a heavy flow while a lowered tube results in a reduced flow.

The glass flow undergoes a “mixing action” created by the rotation of the ceramic tube. This helps to make the temperature consistent while the downward motion of the plunger accelerates the glass flow. This pumping action is timed with the shearing of the glass flow as it falls beneath the feeder to shape the falling gobs. After the gob has been sheared from the feeder it falls into a series of chutes where it is delivered to the blank mold on the I.S. machine.

The I.S. Machine

The I.S. Machine or "Individual Section II Machine" is designed to ensure efficient production so that operators can take one or more sections out of production for repairs without shutting down production in other sections. Gobs enter the I.S. Machine and are formed into containers through a process of controlled shaping and cooling of the glass.

The total time need to produce a container varies, but beer and soda bottles take approximately 10 seconds.
Depending on the container’s size and shape, the machine’s production speed may be as fast as 700 containers per minute.

Parison

A parison is a hollow and partially formed container that will be blown up like a balloon in the blow mold to form a bottle.
It has a cooler skin or enamel outer surface and a temperature of 1700 degrees F on its outer skin.
Parisons are formed on the blank side of an I.S. Machine from gobs and greatly differ in shape for each type of container design.

Container Formation

Manufacturers use three different types of forming processes to make glass containers, depending on the type of container to be produced:

Blow and Blow
Wide Mouth Press and Blow
Narrow Neck Press and Blow

Blow and Blow Process

In the Blow and Blow process, compressed air blows a cavity into the molten gob in the blank mold of the forming machine thereby creating a preform shape known as a parison.
From there the parison is transferred to the blow mold where compressed air is used to blow the bottle into its final shape.

Wide Mouth Press and Blow Process

In the Wide Mouth Press and Blow process, a metal plunger is used to press the cavity into the gob to create the parison in the blank mold.
The parison is then inverted and compressed air blows the container into its final shape. This process is used to manufacture containers with wide finish diameters (38mm and larger).

Narrow Neck Press and Blow Process

The Narrow Neck Press and Blow process is similar to the wide mouth press and blow except the metal plunger in the blank mold is much smaller in diameter. This process is used to manufacture containers with narrow finish diameters (38mm and smaller).
The introduction of this process has enabled glass manufacturers to increase overall productivity and reduce weight and variations in the thickness distribution of beer and beverage bottles.

continue to Section 3.5: Glass Manufacturing Quality

Section 3.5: Glass Manufacturing Quality

Fri, 19 Dec 2008 16:26:32 -0500

Glass container manufacturing quality is a direct correlation to the process controls in place and to standards in which these controls are held:

Batching
Melting
Conditioning
Forming
Packaging
Warehouse
Shipping

Each step in the glass container quality process is subjected to numerous automatic, semi-automatic and manual monitoring and measuring steps both through electronic or human intervention, so as to meet or exceed a customer's requirements.

continue to Section 4: Design & Differentiation