High and low temperature gas actuated cylinder

Details High and low temperature gas actuated cylinder High and low temperature gas actuated cylinder

2001-11-30

2004-02-17

Look, Edward K. (Department: 3745)

Expansible chamber devices

Piston

Side wall portion includes peripheral axially extending...

Reexamination Certificate

active

06691607

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates in general to air pressure cylinders, and more particularly, to air pressure cylinders capable of operation at a broad range of atmospheric/environmental conditions, including extremely high and low temperatures.
In its most basic form, an air pressure cylinder consists of a piston, situated within a cylinder, which is connected to a push rod that exits one end of the cylinder. Ports at each end of the cylinder allow for the flow of pressurized air into the cylinder. When pressurized air is forced into a first end of the cylinder, the pressure in the cylinder forces the piston toward the second end, thereby actuating the push rod. Likewise, when air is forced into the second end of the cylinder, the air pressure forces the piston toward the first end. The push rod moves in synchronization with the piston, and it is the movement of the push rod that is harnessed for mechanical actuation purposes.
The movement of the piston against the cylinder walls creates friction. This friction escalates during continuous use and under conditions of humidity and particulate invasion. In addition, typical air cylinders are composed of metals. When these cylinders are subjected to temperature gradients, each component exhibits a complex set of thermal expansion coefficient characteristics that cause inconsistent expansion in the cylinder. These expansion inconsistencies greatly increase the friction generated in the air cylinder during operation. The friction generated in the cylinder causes wear that leads to degradation and failure. Furthermore, the cylinders can bind or lock-up during extreme temperature operation. These limitations are only exacerbated by the need in virtually all gas cylinders for some form of lubrication. When gas cylinders are used in environments with corrosive chemicals or abrasives, not only do the cylinder components degrade in a very short period of time, the lubrication will typically be compromised or destroyed rapidly by contaminants.
Air cylinders are typically classified according to the distance of piston travel. That is, if the piston in an air cylinder will have a maximum travel in one direction of 2.00 inches, the cylinder will commonly be called a “two inch” cylinder. A complete cycle of operation, in which the piston first travels completely in one direction and then in the opposite direction is considered the “stroke” of the cylinder. Hence, a “two inch” cylinder will have a four inch stroke. Because of this, the life of a cylinder is usually measured by the total amount of piston travel. For example, testing may show that a given two inch cylinder may operate for 500,000 strokes, on average, before failing. This equates to an expected life of 2,000,000 inches (i.e. 4 inches/stroke×500,000 strokes).
The anticipated life for typical lubricated air cylinders range from approximately 3,000,000″ to 4,000,000″, under a moderate temperature and humidity range (i.e. 20° C. to 30° C.; at room humidity) and little or no exposure to particulate or chemical contamination. The life of typical air cylinders degrades rapidly when exposed to more extreme conditions. In fact, because of these limitations, many typical gas cylinders are designed specifically for a single, disposable use.
In many applications, it is desirable for air cylinders to operate for a much longer life. For example, a one inch air cylinder for a push punch along a non-stop assembly line may operate continuously at a rate of 100 strokes per minute. Over the period of one month, the number of strokes for that cylinder will exceed 4,000,000, or 8,000,000 inches. This means that, on average, the cylinder will need to be replaced at least twice each month to keep the assembly line operating. In addition, many applications impart more demanding conditions on the air cylinders with the same desire for long life. For example, a machine to test automobile door handles may require for each test that the test handles open and close hundreds of thousands of times in conditions that include temperature ranges between lower than −70° C. and greater than 110° C., with humidity up to 100% and controlled particulate injections. In such circumstances, cylinder failures not only cause downtime, but can disrupt or ruin ongoing testing. Some cylinders in use in testing facilities need to be replaced on a weekly basis.
Typical air cylinders are also limited in use because they are generally susceptible to a wide variety of chemical attacks. While typical cylinders can be coated or encased in chemically inert materials, and the lubricants and seals can be specially formulated to withstand specific chemicals, these measures are costly and imperfect. They impart inefficiencies in the cylinder, such as additional friction and wear at the seals, that reduce the cylinder life. Similarly, the lubricants in typical air cylinders create the potential risk of contamination in sterile or clean environment applications, such as in food handling or pharmaceutical production. To rectify this problem, a number of concepts have been adopted. For example, special lubricants have been developed for use in certain applications, and cylinders have been developed that operate without lubrication. However, each of these are also costly and imperfect. The special lubricants are more expensive, limited in application, and less effective than normal lubricants, which shortens the life of the air cylinders. The non-lubricated cylinders are more expensive and exhibit a shorter life than lubricated versions.
Finally, typical gas cylinders suffer from a problem commonly known as “bottoming out.” That is, when the piston is allowed to travel the full distance of the stroke under pressure, the piston will violently ‘strike the end of the inner cavity of the cylinder. Because the pistons and housings of typical gas cylinders are made of metals, this impact causes permanent distortions in the piston that can drastically shorten cylinder life or cause a catastrophic failure. Typically, users must “oversize” their gas cylinder purchases to accommodate this problem. That is, if an application requires a 1.5 inch stroke gas cylinder, the user must purchase, for example, a 1.75 inch stroke cylinder and arrange the cylinder such that the required 1.5 inch stroke occurs in the middle of the cylinder's 1.75 inch stroke range. This, of course, is inefficient and costly. Furthermore, any miscalculations will lead to early cylinder failures. While some typical gas cylinders incorporate cushions to soften the impact, this measure is not wholly effective and adds further cost to the cylinder.
Of course, down time in any application is undesirable. However, downtime in production is particularly expensive, since it includes maintenance and parts costs, idle time for workers, reduction in output, and increased pro rata overhead costs. Accordingly, any measure that increases the life of air cylinders without unreasonably increasing the cost of the cylinder is highly desirable.
BRIEF SUMMARY OF THE INVENTION
Briefly stated, a gas cylinder of the present invention comprises a housing defining a cylindrical chamber, a piston within the housing chamber that separates the chamber into two cavities, a rod operatively connected to the piston and which extends from the piston externally of the housing; and one or more gas ports in the housing to allow the input and exhaust of gas in the cylindrical chamber. The addition of sufficient gas, through one or more of the ports, into one of the two cavities of the housing facilitates movement of the piston. Cushions of gas are formed about the piston and the rod, and the piston and rod float in these respective gas cushions,to enable the low friction movement of the piston and the rod within the cylinder housing. Hence, the cylinder can be operated without the use of a lubricant.
A piston seal is positioned about the piston. The piston seal is sized and shaped to facilitat

Affiliated with

Also associated with

Rating

High and low temperature gas actuated cylinder does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with High and low temperature gas actuated cylinder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High and low temperature gas actuated cylinder will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3296871