Understanding Glove Box Technology

29th June 2006

Glove boxes are used to create small controlled environments. They can normally be divided into two different types explained below.

Isolation glove boxes
May be described as a glove box that protects materials or processes from the operator and/or the ambient environment. Isolation glove boxes may be configured to prevent specific kinds of exposure (to humidity, particles, static charges, low or high temperature, etc.).

Containment glove boxes
May be described as a glove box that protects the operator and/or ambient environment from the material or process inside the glove box. Containment glove boxes are commonly used to isolate hazardous materials in the pharmaceutical, biological, and nuclear industries.

These two types of glove box can be combined to create

Controlled Environment Glove Box
May be described as a glove box (either isolation or containment) that meets precise requirements for humidity, temperature, oxygen, static safety, particulates, and/or other environmental conditions. Typically, such enclosures operate under a positive pressure of inert process gas or a negative pressure for fume or other contaminant removal.

Glove boxes meeting these criteria can either be made from Plastics or stainless steel.

Plastic glove boxes.
Plastic glove boxes are normally less expensive than stainless steel but are obviously not suitable where elevated temperatures are concerned and are generally less rugged than stainless steel. Several different types of plastic are available dependant upon the operating processes involved.

Acrylic
Static dissipative PVC
Nondissipative PVC
Polypropylene
Polycarbonate

The size of the glove box is dependant upon the production process and is normally single operator or two operators, access can be gained from either the front or the rear of the glove box or both. Consideration should be given when determining the size of the glove box to the operators reach. Bear in mind that articulation is from the elbow and that limits the areas inside the glove box that the operator can reasonably reach.

Air locks provide a means of inserting and removing product from the glove box without loosing containment. Air locks can be fitted to either or both ends of a glove box and can be configured to meet most process flow requirements. Pretty much the only part of the glove box which will be subject to ware and tear is the air lock doors. These should be on robust hinges, have dual gaskets in a stainless steel frame to prevent warping and rough handling. The latches should be of lift latch type to prevent putting a turning moment on the hinges and causing the doors to drop.

The gloves can be either a bonded sleeve and glove combination which is one piece or a changeable sleeve or glove combination where the final glove is replaceable. The latter is normally preferred as the final glove can be determined to suit the production process and can be replaced when soiled or damaged without replacing the whole glove.

Plastic glove boxes are solvent welded to prevent delaminating and guarantee long life. The thickness of the plastic is sufficient to provide a solid rigid structure and is further increased in the case of negative pressure glove boxes to support higher vacuums.

Glove boxes should sit in a specially constructed frame to support it correctly. Just placing it on a work bench can cause distortion to the glove box if heavy loads are placed inside.

Stainless steel glove boxes.
These glove boxes can be used for many different arduous production processes. Their stainless steel bodies can withstand a range of temperatures, pressure and chemicals and provide a clean air tight controlled environment.

Air locks provide a means of inserting and removing product from the glove box without loosing containment. Air locks can be fitted to either or both ends of a glove box and can be configured to meet most process flow requirements. Pretty much the only part of the glove box which will be subject to ware and tear is the air lock doors. the stainless steel glove boxes feature recessed polyurethane seals and heavy duty latches and hinges for enhanced durability and sealing performance.

Glove boxes should sit in a specially constructed frame to support it correctly. Just placing it on a work bench can cause distortion to the glove box if heavy loads are placed inside.

Glove boxes can simply a sealed space or can be supplied with process control equipment. This can be very simple such as connecting up to a supply of nitrogen to create a low internal humidity environment. Most applications call for some degree of control of the internal environment, a closed loop system is employed using sensors to provide feed back to control equipment. If a glove box is to become a Controlled Environment Glove Box it can be fitted with any of the following environmental process control equipment.

Humidity control
Oxygen control
Vacuum control
Particle and germ control
Temperature control

Humidity control
High purity N2 is introduced into the top of a glove box where it purges out the ambient moisture laden air. There needs to be a valve in the glove box to allow for the gas to flow.

Almost any low RH can be obtained using this system, however nature being what it is will constantly endeavour to equalise the RH between the outside world [high RH] and the atmosphere inside the glove box [low RH]. This will happen every time a door is opened to remove the product, it will also happen gradually over time because plastic glove boxes are made from materials which are Hygroscopic which permit the absorption or passage of moisture. This can be controlled by continually topping up the N2 manually. If this becomes a problem during long production operations or where the specified RH is critical an automated closed loop system must be employed.

An RH sensor is required inside the glove box along with a controller [NitroWatch] connected to a system to turn on and off the N2 flow [DualPurge]. The systems will work together to sense the internal RH of the Glove Box, compare that condition with the specified set point on the NitroWatch and call for more flow of N2 from the DualPurge to returned the system to the desired conditions. The DualPurge is designed to provide N2 at a high flow or purge rate when it is desirable to rapidly recover the set point just after a door has been opened and then to provide a low flow rate to enable the system to toggle around the set point under normal storage conditions. This ensures that the product spends the maximum amount of time at the specified RH whilst minimising the consumption of N2.

This system can provide humidity down to 0.5 ppm[v] for lower levels DewWatch systems must be employed reading Dew Point.

Oxygen control
Similarly where a product process needs to be carried out in a low oxygen environment a O2 sensor can be connected Oxygen analyser and then to the DualPurge which will control the flow of argon or process gas until a set point is achieved. O2 can be controlled in the percentage or ppm range.

Vacuum control
A glove box able to support a negative vacuum must be employed. Our series 200 plastic glove box will support a vacuum down to 5" WG [29.9" Hg in vacuum antechamber] Stainless steel glove boxes can support a vacuum down to 1" Hg. Higher vacuums can be achieved [29.9"Hg in vacuum antechamber] A vacuum control module automatically controls pump action to maintain a stable vacuum inside the chamber. A piezo resistive pressure sensor maintains stability and repeatability.

Particle and germ control
These containment glove boxes have either an "Open-Loop" filtration module where the containment can be safely exhausted to the room or atmosphere or a "Closed Loop" filtration module where the containment is completely re-circulated. These glove boxes incorporate filter fan units mounted on top of the glove box drawing air through a HEPA filter unit.

Temperature control
A wide range of process temperatures can be accommodated from – 40 to +300 degrees C. Glove boxes use double wall insulation to guarantee stable internal temperature platforms. Units are equipped with process gas heaters or coolers for controlled thermal excursions raising or lowering temperatures in minutes. These types of glove boxes can also be equipped with closed loop refrigeration units capable of cooling the glove box down -40 degrees C.