Mar-Bal materials are monitored continuously throughout the manufacturing process. Cure analysis, flow, dimensional change (shrink), specific gravity and weight are performed to ensure the quality of every batch. Physical, mechanical and electrical tests can be performed as needed for specific applications.
Certain grades of Mar-Bal, Inc. molding compounds are highly reinforced with glass fibers and are available only in bulk form, which has a bulky, fibrous consistency. Other select grades are supplied in bulk when it is the preferred form for injection molding.
For most grades, extrusions in diameters of 1” to 4” are available in 6” to 12” lengths. This is a convenient form for automatically cutting transfer and compression molding charge weights while maintaining a minimum inventory of cut slugs. Logs are also easily loaded into injection molding stuffers.
Most extruded products can also be supplied as cut-to=weight charges to facilitate transfer and compression molding. Cut slugs must be between 2” and 12” in length, and weight tolerances are generally controlled to the smaller of ± 5% or ± 15 grams.
The relationship between the length and diameter of cylindrical slugs can be determined from the following equation:
- L = w/(12.86 x D^2 x SG)
- L = slug length in inches
- W = slug weight in grams
- D = slug diameter in inches
- SG = specific gravity of molding compound
Thus, a 250 gram slug extruded through a 2” diameter die in a material of 1.95 specific gravity will yield a slug length of 2.5”. As a general rule, slugs cannon be accurately cut to a weight such that the length will be less than the diameter.
All orders are shipped in packages designed to protect the material in transit and to maintain the desired molding characteristics and endues properties. Depending on the product and form, Mar-Bal materials are packaged in palletized boxes weighing about 50 pounds each or Gaylord containers with individual bags for bulk and injection molding materials.
Shelf life or storage life of all thermoset materials depends on storage temperature. Shelf life will vary depending on the type of product, product form, cure speed, the molding process involved, and the flow requirements of the part to be molded. The recommended shelf life of Mar-Bal materials is two months when stored at 70°F or below. However, many materials maintain moldability for several months. When material is beyond recommended shelf life inspect the material for moldability. If the material’s moldability is in doubt contact your Mar-Bal representative.
Mar-Bal, materials are packaged in special laminated bags which are impervious to the volatile monomers within these products. After the product is removed for molding, the bag should be closed to prevent loss of monomer from the remaining material. Monomer loss in Mar-Bal materials can result in significant loss of moldability and molded properties. Mar-Bal materials are packaged in polyethylene bags within the shipping cartons.
Although refrigerated storage can lengthen shelf life, it is important that the molding compound be allowed to warm to room temperature before opening the container. This will prevent moisture from condensing on the material. If the material has been in cold storage, it should be allowed to warm to room temperature before molding.
Health and Safety Information
Certain Mar-Bal, Inc. materials contain volatile materials which may be harmful if inhaled and may be flammable. These products must be used with adequate ventilation to control vapor concentrations. Read the Mar-Bal, Inc. Material Safety Data Sheet for detailed health and safety information on specific materials.