Heat never vanishes; it is simply transferred from one thing or one form to another, even though there may be a considerable amount of wastage because the recipient of the heat is not ‘gainfully employed’. How does this affect the work of a caster operative? He should remember that heat is a form of energy: like electricity, it can be transformed from one state to another. Temperature is simply a measurement of the intensity of heat, not its amount, so there’s more heat in a good cup of tea than there is in a red-hot penny, though the temperature of the coin is far higher. Furthermore, heat always flows down from a higher temperature level to a lower. In the pot of the caster, type metal is heated—generally by electrical elements—to melting point and beyond so that it will flow readily into the corners of the casting cavity in the mould and, more important, into the matrix impression, so that every detail of the character is reproduced. If the mould is opened immediately and the contents pushed out, there will be an unpleasant mess of congealing shapeless metal, but nothing resembling the required piece of type. Before attempting to eject the type, we must give it time to solidify; by transference of heat to its surroundings, its temperature must be lowered till it is below its melting point and the metal possesses adequate mechanical strength. How long this takes depends on many things, including the ratio be- tween the volume of the cast character and the area of mould-walls with which it is in contact, the respective heat-conductivities of the type metal and the mould, and, of course, the extent of the necessary fall in temperature. The greater the difference in temperature between the ‘giver’ of the heat and the ‘receiver’, the more quickly does the flow occur.

From this, we learn that large types must take longer to solidify than small—in fact we know well that they do—that type metal should never be heated more than is necessary to give a free flow, and that the walls of the casting cavity should be kept as cool as possible, commensurate with good surface-finish on the product.

The size of type we can do nothing about, as it’s specified according to the requirements of the job. But we can control the temperature of the inflowing metal, remembering that there is an optimum point between (on the one hand) the sticky mass from a still-warming-up pot or an over-cooling due to an excessive charge of unwarmed metal and (on the other hand) the excessive temperature which, it is hoped (but vainly), will overcome some other defect such as a partly blocked nozzle. We can also regulate the rate of casting.

Cooling the cast

So we come to the components that bound the casting cavity: six faces that collect heat from the type metal. Two of the sides are mobile, the crossblock and the mould blade. The floor is the step of the crossblock, and the ceiling is the matrix which is being constantly changed and so has a chance to cool off. There remain the two side blocks, with metal-flooded areas that fortunately vary with the set-width of the character being cast. These blocks are provided with internal water-ways through which a controlled stream of coolant can flow, and this is where the greater part of the cooling of the mould takes place.

If we could keep a fast-flowing stream of ice-cold water rushing into the mould passages, we should be able to reduce the solidifying time and so increase the safe running-speed of the caster, but there has to be a compromise. Too low a temperature, and the surface of the type is affected; it becomes ‘frosted’: let the mould get too hot, and the crossblock will start to cut the tang before the metal in the centre of the type has solidified, and ‘bleeding feet’ will result. So the regulation of the flow is a matter of importance.

The water-course

Check the path of the water. The in-flow pipe leads to a filter in the base and then to the first supply valve by which the water can be shut right off before it gets near the mould. Be sure that this is ‘off’ every night, particularly at week-ends and preferably during lunch breaks or any other shut-down of an hour or more. This will relieve the joints in the mould from pressure which otherwise might lead to gradual seepage of the water to areas where it could cause damage. Any good operative will drain the mould, blow out the water and force some oil through before a lengthy shut-down.

Close above this supply valve is a similar one; used to regulate the whole of the flow into the main part of the system; when adjusted, this need not be disturbed, as ‘on-off’ is controlled by the first valve.

A pipe leads to the front water connection at one end of an L-shaped duct in the main stand, taking the water to the side water pipe connection on the right. This connection has internal passages which make it also a distributor there are two inlets and three outlets.

The cool in-coming water is divided into two streams, one of which goes to the mould (as described below) while the other is piped to an escape valve on the front of the machine. If this is closed, the entire flow is compelled to pass through the mould, giving maximum cooling, but, when open, it allows a large part of the flow to escape, thus enabling the mould temperature to rise. The released water falls into an open collecting head (the pipe bracket) and it then goes to waste.

Water not so released is directed back into the main stand where it travels up through a brass duct in a stainless steel pad to the base of the mould. Here the route is by way of internal passages drilled in the intermediate plate to the upward-sloping duct in the screw- side block. The top of this runs into a vertical duct bringing the water back to—and then through—the intermediate plate. A channel in this leads to the base of the vertical drilling in the nick-side block. As in the screw-side block, this communicates with a sloping duct, returning the water (with the heat it has abstracted from the side blocks) by way of the intermediate plate and the base, to a second brass-lined drilling in the pad.

Unobstructed channels

For convenience, the water is again brought up to the side connection though not to mix with the other streams; thence by pipe to the collecting-head and so to waste. Waste, that is, so far as the caster is concerned, but it is very probable that we are not dealing with ‘raw’, untreated water. Today, more than ever important to ensure that water-ways remain clear. Before the introduction of the constant-height pattern composition mould, it was customary for moulds to be returned after every 2,000 hours’ work—or thereabouts to the Monotype Works for renovation of the matrix-seating face. Whether the owner knew it or not, it was our practice to clean out all the water-passages at the same time, and some of them were in a sorry state. Now that moulds come back less frequently, it is essential to see that their internal condition is carefully and constantly safe-guarded.

Water from the mains will be quite suitable for drinking — and indeed beneficial — but it may be very injurious to a mould.

In areas where the water is hard, it must be treated before being used for cooling. Otherwise, lime, which forms the grey fur in kettles, will certainly build up in the waterways of moulds, and eventually lead to overheating, and consequently to faulty type. In other districts the water may be soft but aggressive, and cause rapid corrosion of mould surfaces exposed to it. By using, as the coolant, distilled water containing a corrosion-inhibitor, troubles due to corrosion or blockage of the waterways are eliminated. We recommend an initial make-up of 0.5% sodium chromate (½lb sodium chromate for each 10 gallons of distilled water). Losses due to evaporation should be made good with distilled water. Sodium chromate is a poison; therefore, care should be exercised when making up the solution; for example, by wearing protective gloves, by not inhaling dust from the compound, and by avoiding splashes from the concentrated solution.

A small minority of persons are allergic to chromates and it is advisable that operatives should wash their hands should they come into contact with the coolant.

As the duty of the water is simply to carry away heat, and it is not otherwise affected, it can be re-used repeatedly as soon as it has ‘unburdened itself’. And since it is now a good deal more valuable than tap-water, it should: by use of a closed-circuit cooling system, it can.

Closed circuits

Because the components of such a system can easily be supplied and fitted up by a local plumber, we do not provide them, but drawings and data are readily available. The main requirements are three tanks, a small electric pump and piping. The supply tank should be in a raised position so that it can give a gravity feed by pipe to the water-intake in the base of the caster. The pump-feed is connected to the storage tank, fed from the out-flow (the so-called ‘waste’) from the caster, and piped so that it delivers the water back to the supply tank. A small priming tank, ancillary to the pump, ensures its constant readiness.

Radiation and convection disperse the heat, so that the supply, taken from the bottom of the supply tank, is always cool. A good current of air will absorb the heat, but, if earth surrounds the storage tank, it will do so more effectively. Measured from the surface of the water in the supply tank to the mould on the caster, the height should not be less than 12 ft, to give a working pressure of about 6 lb/sq. in. Pipe-diameter must be sufficient for a free flow to each caster.

Alternatively, it may be more convenient for the coolant to be pumped through a pressure-relief valve and thence direct to the machine, without any upper tank. In this case, as there is no gravity feed to maintain the flow should the pump fail, it is desirable to install a duplicate. Consequently the same non-aggressive water can be used repeatedly, with only loss by evaporation or by accident to be made good, but failure to treat the water on the principle described can all too easily lead to exasperating and expensive troubles with the mould.

Non-scientific readers of medical handbooks sometimes imagine themselves afflicted with all the ills described and develop into hypochondriacs. We hope that a comparable result will not be the consequence of this article. Disposal of the heat from casting has undoubtedly presented problems but prolonged research has solved most of them, so that the profitability of our casting equipment has advanced through the years. To define a difficulty is the first step towards overcoming it, and our pursuit of fresh improvements is unending. Meanwhile, our service inspectors are always ready to advise on individual requirements.