Glassmaking Process

*Video:video for glass manufacturing

This process uses state of the art equipment to cool and shape molten glass into a desired form. While the art of glass making dates back to around 1500 BC, modern glass container production did not occur until the late 19th century. The glass container manufacturing industry continues to advance its craft in order to deliver higher quality products in a more efficient manner.

Click on the video to the right to watch the glass manufacturing process in action. More information on the glass manufacturing process and steps can be found in the diagram and text below.


Glass Manufacturing Process Diagram

Click on the image to enlarge

Mix and Melt

The glass making process starts out at the batch house, where raw materials arrive via truck or rail, are carefully inspected, and then elevated into the proper storage silos. The raw materials are weighed and sent to the mixer, which is located just above the furnace. Cullet, or recycled glass, is introduced to the mixture and composes 15% to 55% of the batch. The batch mixture is then transported by either a horizontal conveyor belt or monorail train to the furnace.

The furnace consists of three main parts: the melter, the refiner, and the forehearth. The batch is fed into the furnace at the same rate as it is pulled out of the feeder. As it travels through the furnace at an average temperature of more than 2,300 degrees, its depth of around 4 or 5 ft must be maintained to within 0.01 of an inch. Furnaces can range in size from 450 to more than 1,400 square feet of melter surface. With the help of gravity, the molten glass flows through the refiner out along the forehearth, where it is carefully cooled to a temperature and desired viscosity before reaching the feeder.


Once to this position, the molten glass flows through a hole in the bottom of the feeder. The amount of molten glass allowed through the feeder is controlled by a ceramic plunger, which is timed with a shearing device that cuts the glass flow as it exits the feeder. The shearing creates a specific amount of molten glass, known as a gob, which will be formed into individual containers. The gob now travels down to the Individual Section Machine (I.S. machine).

Each machine can have anywhere from 4 to 20 sections, each capable of producing 1 to 4 bottles simultaneously. The gob drops into the blank side mould, which produces a hollow and partially formed container, known as a parison. From here, manufactures have three different types of forming processes to choose from, depending on the type of container being produced.

The three processes are Blow & Blow, Wide Mouth Press & Blow, and Narrow Neck Press & Blow. During the Blow & Blow process, compressed air forces the molten gob into a partially formed container in the back side of the forming machine. The Press & Blow processes use a metal plunger to shape the gob, allowing for manufactures to increase the overall productivity and reduce weight and variations in the thickness of beer and beverage bottles. The parison is now inverted over to the blow mould, where compressed air blows the container into its final shape.

Once released from the moulds, the bottles then cross the cooling plate where the temperature drops to around 900 degrees. They are then loaded into the annealing lehr, which brings the temperature back up to near melting point, then slowly reduces the temperature to below 900 degrees. This process, along with hot and cold end sprays, relieves stresses caused by the rapid cooling and produces stronger, more shock resistant containers.


While traveling on to their final destination, the containers pass through a number of inspection instruments, which optically and physically test the containers for defects. Each and every container passes through this automatic inspection equipment where the side thickness is measured; the finish (i.e. the “top” of the container) is inspected for defects, and the overall measurements are compared against the specifications for that particular container. Depending on the type of container other inspections may be done such as pressure testing for pressurized containers and a shock test for items that are to be filled with hot materials by the customer. Any container that does not meet our strict quality criteria is immediately rejected.

The rejected bottles are sent back as cullet (crushed glass) and melted to start the process all over again. Bottles that pass the inspection continue on their journey to be packaged for eventual delivery to the customer.

Packaging and Shipping

At the end of our production lines there are two packaging options: bulk packaging or carton packaging.

Bulk Packaging: Bulk packaging consists of packing the glass containers directly on pallets with corrugated sheets between each layer. This is a simple, efficient option chosen for many high-volume glass packages. Items packaged in bulk are arranged anywhere from 5 to 15 layers per pallet depending on stability. Once pallets are built, plastic bands or straps are fitted to the pallet and the entire unit is sent to the stretch-wrapping unit to apply plastic wrap for added stability.

Carton Packaging: Carton packaging consists of packing the glass containers in our customers’ shipping cartons. In this case, cartons are purchased and formed at our plant. Glass Containers are inserted either necks up or necks down in the carton and the cartons are then stacked on pallets or corrugated sheets. Once pallets are built, plastic bands or straps are fitted to the pallet and the entire unit is sent to the stretch-wrapping unit to apply plastic wrap for added stability.

The finished product, once palletized, is transported via forklift or stack train to either awaiting trucks or to its designated position within the warehouse until requested by the customer. Once requested, the items will be picked from the warehouse and carefully loaded onto trucks for transport to the customer.