Case Air Seal
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A well-sealed case limits the entry of air, dust and insects and reduces the air exchange between the display chamber and the exhibit room. Infiltration generally occur at exhibit case seams and joint, there- fore the case design and fabrication must ensure:
- precise fitting construction joints and seams;
- use of appropriate and conservation acceptable gaskets and caulk sealants.
Gaskets should be used at the interface of adjoining surfaces such as removable panels, doors and glazing. A wide range of elastomer materials and designs are available, however, not all can be recommended:
- avoid unsafe or untested materials;
- avoid the use of gaskets with unknown adhesive backings.
Gasket Applications: Compression
An effective seal requires appropriate design/engineering for the specific application. This includes:
- correct thickness - an appropriately sized gasket allows for uniform seating of surfaces yet does not hold them apart;
- correct density - an appropriate degree of softness allows conformity to opposing surfaces;
- appropriate compression - case design should ensure closure does not over compress the gasket.
As a rule of thumb, gaskets can only be compressed in one direction effectively. Avoid designs that pinch or slide case against the gasket surface. Where possible, utilize a recessed channel to control the depth to which the gasket is compressed.
Gasket Applications: Corners and Hinges
Well-sealed cases frequently experience gasket failure at corner and at hinge locations. Select the right method of application: careful mitering of gaskets at corners is required, and gasket lengths should be cut longer than necessary. Doors and removable panels require continuous door stops. Where possible, use lift-off doors and panels which are easier to seal than conventional hinges that bind. Large doors require specialized designs and individual fittings. Mock-ups and prototypes are very useful to evaluate door and corner gaskets performance.
Case Sealing Techniques
Effective solutions for sealing cases requires thoughtful design, th whenever possible, the development of prototypes. The following pages illustrate several practical designs using a variety of hardware, gasket types and construction techniques. Effective designs and careful assembly can over- come the most commonly occurring challenges:
- creating effective seals around fixed glazings;
- selecting the appropriate surface to gasket;
- creating continuous and smooth stops for doors;
- using sufficient fasteners to seat movable components without uneven or excessive compression;
- placement of fastening screws and bolts that do not disrupt the case seal.
The following figures illustrate several practical designs using a variety of hardware, gasket types and construction techniques.
Most display cases in the past were unsealed. No attempt was made to seal seams and joints to reduce air exchange; air movement was controlled by natural convection. These designs are still used where the exhibit space atmosphere meets the conservation criteria - these cases do not provide any protection from the entry of dust, pollutants, insects, or unstable room climate. A large variety of frame designs are commercially available for use in unseal case construction. "Positive pressure" case designs utilize unsealed case construction together with a forced air system.