Time for cure

Comparison of Experimental and Theoretical Time for Cure in IR Oven... 

Figure 8. Plot of log10 viscosity vs. time for curing systems. Key , 3407 O, 3330 A, 3327 +, 3328.

The goal of treatment of erysipelas is rapid eradication of the infection. Mild to moderate cases of erysipelas are treated with procaine penicillin G 600,000 units intramuscularly twice daily or penicillin VK 250-500 mg orally four times daily (in children 1-18 years of age, 25,000-90,000 units/kg per day divided into four doses) for 7 to 10 days. " Penicillin-allergic patients can be treated with clindamycin 150-300 mg orally every 6 to 8 hours (in children, 10-30 mg/ kg per day in three to four divided doses). For more serious infections, the patient should be hospitalized, and aqueous penicillin G 2-8 million units daily should be administered intravenously. Marked improvement usually is seen within 48 hours, and the patient often may be switched to oral penicillin to complete the course of therapy. One randomized, double-blind, placebo-controlled study showed that the median time for cure, intravenous antibiotics, and hospital stay was reduced in patients receiving prednisolone in addition to antibiotics. Further studies are needed, however, before corticosteroids can be recommended for routine use/- ... 

Figure II. Graph of peak area ratio (1731 2250 cm-1) against time for curing of simulated rocket fuel with urethane binder.

Introducing the adhesive onto the production line requires great care as an inadequate understanding of the material and its properties may cause unnecessary difficulties. Common mistakes are the use of too little material and not allowing enough time for cure. Sometimes, quite inappropriate tests are devised and in consequence the performance is misjudged. 

Great care is required for both comparative testing and standardisation, where it is vital to avoid subjective assessment, particularly where measured performance depends largely on variables such as the surface and its finish ductility of the metal involved degree of contamination distance between mating surfaces temperature viscosity of the adhesive and time for curing. 

Figure 2. Contact angle values versus time for cured PDMS and different kinds of cured PDMS-b-PEO copolymers where the size of the PDMS block was 6000 for every sample and the size of the PEO block varied A = 270 g/mol, = 330 g/mol, = 520 g/mol, = 1350 g/mol. o = PDMS film. All the films except the one marked with filled square ( ) were single phase.

Time for curing heavily dictates achievable production rate tapes are instant, cyanoacrylates take several seconds, anaerobics can take 15-30 min, epoxy resins may take 2-24h, although this can be reduced using catalysts. 

A demand of the industrial practice is that the time for curing an adhesive should be as short as possible. But often different requirements of the complete process anticipate the use of a quick curing adhesive. For this reason methods were developed enabling the user to handle the adhesive as long as needed and to cure within seconds or minutes after having joint the adherends. 

Vulcani2ation is a chemical process for improving an elastomer compound s performance. However, in most cases not all of the desired properties reach their optimum levels simultaneously. One of the mbber compounder s key responsibiHties is to achieve a balance of the most important property requirements by the proper selection of cure system (chemical) and time—temperature cure cycle (physical). 

Preparation of paint, its viscosity, solvent, thickness of one coat, air pressure, curing temperature and time of curing will remain the same as for the primer (Table A13.4). 

The temperature and time of curing, as indicated in Table A 13.4, are indicative and for general guidance only. They may vary with the type and quality of paint and effectiveness of the furnace. For exact details, consult the paint manufacturer. The operator may also vary the given parameters slightly, based on his own experience and the end results. 

Urea-formaldehyde powders have a limited shelf-life but some improvement is made by incorporating a stabiliser such as hexamine into the moulding power. In some formulations the cure rate and the related time for flow are controlled by keeping the latent acid catalyst fixed and adjusting the stabiliser. 

The ebonite compound before cure is a rather soft plastic mass which may be extruded, calendered and moulded on the simple equipment of the type that has been in use in the rubber industry for the last century. In the case of extruded and calendered products vulcanisation is carried out in an air or steam pan. There has been a progressive reduction in the cure times for ebonite mixes over the years from 4-5 hours down to 7-8 minutes. This has been brought about by considerable dilution of the reactive rubber and sulphur by inert fillers, by use of accelerators and an increase in cure temperatures up to 170-180°C. The valuable effect of ebonite dust in reducing the exotherm is shown graphically in Figure 30.3. 

Bond strength can vary from a temporary bond (non-curing compound) to a substrate tearing bond (using phenolic-modified curing products). Solvent-borne CR adhesives can be formulated to have very short open times for fast production operations or to retain contact bond characteristics for up to 24 h. Heat and solvent reactivation can be used to re-impart tack to dried surfaces. 

The advantage of sol-gel technology is the ability to produce a highly pure y-alumina and zirconia membrane at medium temperatures, about 700 °C, with a uniform pore size distribution in a thin film. However, the membrane is sensitive to heat treatment, resulting in cracking on the film layer. A successful crack-free product was produced, but it needed special care and time for suitable heat curing. Only y-alumina membrane have the disadvantage of poor chemical and thermal stability. 

---