How to blow glass with a butane torch
There have been many articles written over the years about how to choose the right glass blowing torch; this article, which was originally written by Henry Grimmett and published in Glass Line Magazine is focused on how to set up your glass blowing torch. The setup often turns out to be more influential on the outcome of your work than the original choice of glass blowing torch, and for this reason the lampworker must understand the fundamental factors involved.
Gasses used by your glass blowing torch
Unless you are working on a Hothead there is a fuel and an air or oxygen supply. These gasses pass through orifices and valves in the regulators, then through supply lines to more valves at the torch and then through burner tubes (orifices) and hopefully burn in a smooth laminar flow.
The fuel gas is often propane or natural gas but can also be butane or mapp gas among others. For the purpose of this article, the focus will be on propane gas. References to oxygen also apply to the use of air.
The setup of your supply line hoses is of extreme importance. In an attempt to save money, one may choose a smaller diameter hose/pipe thinking that 20 pounds of pressure is 20 pounds of pressure, not considering the pressure drops associated with the various diameters of supply lines, or the volumes that can actually be transported through these long tunnels.
Another common problem is selecting the proper diameter but the wrong material and as a result suffering with glass blowing torch performance issues due to the side walls of the hose/pipe sloughing off material that plugs the valves and burner tubes of the torch from the gas supply side.
Selection of the valves and regulators is also of great importance because they are the primary controls of the gas flow from the source to the torch. Should they be single or two-staged, low pressure or high pressure? When using a manifold for several torches where should the regulators go in the setup?
Putting It All Together
First, if there are employees involved then there are many additional legal responsibilities involved. It is important to have documented training programs and written testing on how to properly use propane and propane tanks, how to handle oxygen tanks and regulators and how to inspect supply lines for wear and tear. Either the trainer has to be trained by attending seminars or an outside consultant needs to be brought in to provide the training. Consider contacting your vendors and asking them if they have a program that will meet your needs.
If operating multiple glass blowing torch hard-lines, such as copper or stainless steel, tubing should be plumbed in. Never use PVC, especially for the fuel gas. (Note that a poorly installed propane system may cause a potentially dangerous or life-threatening situation and all building codes should be followed. If you install the hard line system rather than using the services of a professional then be familiar with National Fuel Gas Code, ANSI Z 223.1and the National Fire Protection Association (NFPA) 58.) Some of the basics include: always use flare fittings, isolate copper tubing from contact with other metals (to prevent electrolytic corrosion), separate gas lines from electrical conduit by a minimum of four inches and consider additional shut off valves for the fuel gas, especially if the tank and regulator are outside.
When using flexible supply line such as welding hose or reinforced clear polyurethane tubing such as Tygothane® it is important to verify that the material can be used with propane under pressure. If the hose material is purchased from a hose supplier, rather than a nationwide discount store, obtaining the brand name, part-number and specification sheet is generally very simple. Sometimes a call to the manufacturer is necessary to answer a very specific question. At GA we selected a 1/2 inch I.D. reinforced Teflon tubing with braided stainless steel cover for flexibility, heat and abrasion resistance and very high pressure ratings.
To achieve laminar flow, the basic goals when setting up the glass blowing torch are to know that enough volume of gas is being delivered and to be able to stabilize the flow. By utilizing a regulator or flow-valve at the tank and an in-line regulator mounted at the bench you can ensure adequate volume and control. From the first stage to the second choose a supply line bore based on the number of torches, for example 1/4 inch would support one larger glass blowing torch or two smaller glass blowing torches while 3/8 inch might support three larger glass blowing torches. From the in-line regulator to the torch use a bore size that will slip onto the fitting supplied with the torch keeping the length to a maximum of about four feet. If only the first stage regulator is being used and the desire is to improve color results use the shortest supply line lengths possible. In the case of a propane tank that is stored outside consider using a larger bore size and a protective shelter to minimize temperature fluctuations.
To summarize, it is important to know the demand of the glass blowing torch for gas and air in an all-out situation. The regulators need to be capable of supplying this demand. Due to pressure drop issues, supply lines should be short and of significant enough bore to deliver the demand volumes. Simply increasing the pressure to get more juice is very similar to over pumping the beer keg. The same thing happens in the torch, the laminar flow becomes turbulent and the flame consists of hot and cold spots. It takes longer to pull points, build sculpture and the colors become dull.
When the glass blowing torch is set up properly and the correct propane and oxygen settings are chosen the colors are no longer dull, rather they remain bright.
There have been many articles written over the years about how to choose the right glass blowing torch; this article, which was originally written by Henry Grimmett and published in Glass Line Magazine is focused on how to set up your glass blowing torch. The setup often turns out to be more influential on the outcome