Mold life time

Figure 5.2 shows the resulting choices for the material of the injection mold and the resulting mold life time, measured on the basis of the qualitatively achievable injection cycles. 

Ca-stearate (HALS-III, without AO-II). Test specimens compression-molded plates (2.0 mm thick). Weathering test sunshine carbon arc lamp weather meter (WEL-SUN-HC, Suga Test Instruments Co., Ltd.). Black panel temperature 63 3 C, without water spray. Failure criterion time to 507, loss of original elongation (half life time = H.L.T.). IF = H.L.T. with stabilizer/H.L.T. without stabilizer. (b) Test specimens compression-molded sheets (0.5 mm thick). Aging test forced air circulation oven at 150 C. 

Series molds are designed according to the number and life time of products. The number of cavities and the process and degree of automation are defined according to the product specification. The series molds are mostly manufactured from hardened steel (up to 65 HRC) and are coated with for an optimization of the demolding process as well as the service life. 

Another consideration in raising the mold temperature is the longevity of the mold itself It has been dem-onstratedl" that operating the mold at extreme temperatures, even in the absence of thermal degradation of the plastic, affect the mold life and maintenance costs detrimentally. The balance of cycle time reduction and cost increase is unfavorable, especially for resins such as fluoropolymers that require high temperatures. 

Chocolate (0.3—0.5% lecithin) lecithin is a wetting agent and emulsifier. It facihtates mixing, saves processiag time and power, saves cocoa butter, stabilizes viscosity, iacreases shelf life, counteracts moisture thickening, and aids release of molded goods (see Chocolate and cocoa). 

An important aspect of this procedure is the use of latent acid catalysts, such as phenyl hydrogen maleate, phenyl trifluoracetate, and butadiene sulfone. These catalysts reduce the peak exotherm from over 200°C to 130—160°C. The resin catalyst mixture has a working life of up to several days at RT. The elevated temperature of mol ding these latent catalysts generates the corresponding acids, namely, maleic, trifluoracetic, and phenolsulfonic, which cataly2e the resole reaction. Typically, a cycle time of 1—2 min is requited for a mold temperature of - 150° C. 

Extended pot life Void-free uniform, long flow time in mold before gel. Large complex moldings. 

An early application for the propionates was that of dipping Cheddar cheese in an 8% propionic arid solution, This increased mold-free life by 4 to 5 times more than when no preservative was added. For pasteurized process cheese and cheese products, propionates can be added before or with emulsifying salts. Research has indicated that propionate-treated parchment wrappers provide protection for butter. 

Once the prepolymer and catalyst are added together, the chain extension (curing) reactions will commence. The time taken to mix must be carefully monitored. It must be sufficient to allow complete mixing, but there must be enough pot life left to allow pouring into the mold while the material is at the lowest viscosity possible. This is to allow the polyurethane to fill the mold completely and any entrapped bubbles to reach the surface. 

Several factors must be taken into account when the exact grade of material is chosen. The first is the pot life of the system. The pot life controls the time it takes to fill the mold, allowing any entrapped bubbles to rise and to gel off so that it can be placed in the curing oven. This represents a large portion of the physical cycle time. 

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