One shot

With the use of suitable catalysts, it is possible to produce a polyurethane product in a single step. This involves the mixing in the correct ratios of the polyol(s), isocyanate, catalyst, and any pigment and plasticizer. 

A major problem is the exotherm that is given out in the reaction. The heat generated must be removed in the molding. The total amount of heat given out is the sum of the heat from the initial prepolymer reaction and the final chain extension stage. This leads the process to be used in relatively thin-walled products. 

Alliance for the Polyurethane Industry, TDI Transportation Guidelines, (2002) Arlington, VA American Plastics Council. 

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If the inspection equipment can be run under stable and reproducable conditions due to the QAP the basis for using a camera system for flaw detection is given.The camera system consists of CCD-cameras and a pattern recognition software. Up to four CCD-cameras can be served by one PC. One shot of the part may be copied up to 16 times in the computer and this theoretically enables the crack determination with 16 different parameter sets. 

Monomer emulsions are prepared in separate stainless steel preemulsification tanks, which are usually equipped with an agitator, manometer level gauge, cooling cods, temperature recorder, mpture disk, flame arrester, and various nozzles for charging the ingredients. Monomer emulsions maybe charged in one shot to the reactor or, more commonly, fed continuously throughout the polymerization. 

In the Shoe or one-shot method (4), formamide is used to coagulate sodium silicate. The silicate solution used in the Joosten method can be diluted with water to lower its viscosity. Concentrations of sodium silicate between 10—70% are used (viscosities of 2.5—50 mPa-s). Concentrations of formamide are between 2 and 30%. Other reactants such as CaCl2 and sodium aluminate are used in concentrations between 2.4—12 g/L of silicate solution. 

In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

A variation on this method is ealled the shut-down on overcurrent eireuit shown in Figure 3-48. Here the start-up eireuit is a diserete, high-voltage, one-shot eireuit that is aetive only during the start-up sequenee, but turns eompletely off thereafter. If an overeurrent foldbaek eondition is experieneed, the IC and drive eireuits no longer have a voltage supply from whieh to draw eurrent. This... 

The MC34067 data sheet eontains the neeessary equations and graphs in order to set the eritieal timer funetions of a ZCS QR eonverter. Some of the times, sueh as the one-shot off-timer, will have to adjusted in the breadboard stage. 

The one-shot timer can be set entirely from a graph and the approximate values from the graph are RT = 1.5Kohms and the CT = 220pF. 

Because of their importance in foam manufacture, one-shot systems are dealt with in more detail in Section 27.5. With solid materials the systems are used for... 

Polyurethane foams may be rigid, semi-rigid or flexible. They may be made from polyesters, polyethers or natural polyols such as castor oil (which contains approximately three hydroxyl groups in each molecule). Three general processes are available known as one-shot, prepolymer or quasi-prepolymer processes. These variations lead to 27 basic types of product or process, all of which have been used commercially. This section deals only with flexible foams (which are made only from polyesters and polyethers). Since prepolymers and... 

The one-shot polyethers now form the bulk of the flexible polyurethane foam now being manufactured. This is a result of the favourable economics of polyethers, particularly when reacted in a one-shot process, and because the polyethers generally produce foams of better cushioning characteristics. A typical formulation for producing a one-shot polyether foam will comprise... 

The secondary hydroxyl groups of these poly(oxypropylene) glycol diols are less reactive than the primary hydroxyl groups of the earlier polyesters. At the time of the introduction of these polyethers, the catalysts then available were insufficiently powerful for one-shot processes to be practical and so these polymers have been used primarily in prepolymer processes. 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

Surface active agents are important components of foam formulations. They decrease the surface tension of the system and facilitate the dispersion of water in the hydrophobic resin. In addition they can aid nucleation, stabilise the foam and control cell structure. A wide range of such agents, both ionic and non-ionic, has been used at various times but the success of the one-shot process has been due in no small measure to the development of the water-soluble polyether siloxanes. These are either block or graft copolymers of a polydimethylsiloxane with a polyalkylene oxide (the latter usually an ethylene oxide-propylene oxide copolymer). Since these materials are susceptible to hydrolysis they should be used within a few days of mixing with water. 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

In addition to one-shot processes, quasi-prepolymer systems are used commercially with rigid polyether foams. The quasi-prepolymer is commonly produced using excess TDI rather than diphenylmethane di-isocyanate. Sinee the former isocyanate is light in colour and the latter dark, quasi-prepolymer foams... 

Because of the high cross-link density of polyisocyanurates as prepared above, the resultant foams are brittle, so that there has been a move towards polyisocyanurate-polyurethane combinations. For example, isocyanurate-con-taining polyurethane foams have been prepared by trimerisation isocyanate-tipped TDI-based prepolymers. The isocyanurate trimerising reaction has also been carried out in the presence of polyols of molecular weight less than 300 to give foams by both one-shot and prepolymer methods. 

The safety "campaign" must not be a one-shot exercise because then the effects will be short-lived (not more than 6 months). This makes the use of such campaigns costly in the long nm despite the initial appearance of a cheap solution to e problem of human error. 

The macroazoinimer obtained by the end capping reaction of polyazoester with a diizocyanate and hy-droxyethyl methacrylate was used in wood impregnation leading to the one-shot polymerization of styrene thermally [50]. 

Automatic lubrication systems may be divided broadly into two types circulatory and one-shot total-loss. These cover, respectively, those components using relatively large amounts of oil, which can be cooled, purified and recirculating, and those in which oil or grease is used once only and then lost. Both arrangements may be used for different parts of the same machine or installation. 

There are many kinds of loss-lubrication systems. Most types of linear bearings are necessarily lubricated by this means. An increasingly popular method of lubrication is by automatic or manually operated one-shot lubricators. With these devices, a metered quantity of oil or grease is delivered to any number of points from a single reservoir. The operation may be carried out manually, using a hand-pump, or automatically, by means of an electric or hydraulic pump. Mechanical pumps are usually controlled by an electric timer, feeding lubricant at preset intervals, or are linked to a constantly moving part of the machine. 

On some machines both hand-operated and electrically timed one-shot systems may be in use, the manual system being reserved for those components needing infrequent attention (once a day, for example) while the automatic systems feeds those parts that require lubrication at relatively brief intervals. 

One-shot metered lubrication is eminently suited to oiling systems and can be employed either in an all-loss arrangement or as part of a circulatory system. Sight-glasses or other indicators should be incorporated since such lubricating mechanisms are nowadays so reliable that a blockage or other failure might not be suspected until too late. 

Consolidation Even though blow molding provides the capability of providing multiple products combined into one, by including hinges the designer has an added feature. The ability to produce many articulated products in one shot has always opened new design... 

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