CHAPTER XIII.

PAINT MACHINERY.

In Fig. 40 is shown a complete set of paint grinding and mixing machinery, made by Wright & Co., 157 Southwark Bridge Road, London, S.E., which has given highly satisfactory results in efficiency and economy. It has a set of three granite rollers 30 inches by 15, and two mixing cylinders or pugs, 24 inches in diameter by 25 inches deep, the whole mounted on a strong cast-iron frame. It is made in the following five sizes:--

---+----------------+---------+---------+----------+------------------------- | | | | | Work turned out per day. No.| 3-roller Mills.| Diam. of| Speed of| Weight. +------------+------------ | Size of Roller.| Pulleys.| Pulleys.| (Approx.)| Ordinary | White | | | | | Colours. | Lead. ---+----------------+---------+---------+----------+------------+------------ | in. in. | in. | | cwt. | tons. | tons. 1 | 16 × 9 | 18 | 70 | 12 | ½ to ¾ | 1½ 2 | 22 × 12 | 24 | 60 | 16 | 1 “ 2 | 4 3 | 22 × 14 | 26 | 55 | 22 | 3 “ 4 | 8 4 | 30 × 15 | 30 | 50 | 30 | 4 “ 5 | 10 5 | 36 × 16 | 30 | 50 | 35 | 5 “ 6 | 12 ---+----------------+---------+---------+----------+------------+----------

The utility of having the pug mills placed above the granite rollers is to save labour and space, and the roller mill is kept constantly at work. There are two pugs, one of which is always ready to deliver to the rollers, whilst the other is getting ready by the time the first is being emptied; by this means the output is always going on, and hence great saving both of time and labour. The pugs are

easily fed from a wooden stage fixed to the frame at the back of pugs. The drawing shows the gear driven by a cog-wheel, but if required it can be driven by fast and loose pulleys. The whole of the machine is very compact.

A handy little grinding machine by the same well-known firm is shown in Fig. 41; a liquid-paint mixer, in Fig. 42; and a single pug mill for paint or putty, in Fig. 43. Neither of these machines requires any special description, as the mode of application is evident from the illustrations.

This firm are also the manufacturers of Clark’s patent paint mill, illustrated in Fig. 44. This mill differs from the ordinary mills in having five instead of three rollers. The material is fed in between the two uppermost rollers, being prevented from spreading too much by means of wooden cheeks shaped so as to fit between the rollers and form a kind of hopper in which the material to be ground is placed. From these two rollers it passes to a third and

fourth placed below, and receives a final grind from the fifth roller in front of the machine, from which it is delivered to the spout as shown. The rollers are all of granite turned truly cylindrical. They are 15 inches in diameter and are mounted on strong steel spindles. These spindles run on bearings working in guides, by means of which the distance

apart of the rollers and the fineness of the grinding can be adjusted. It will be seen that the driving-shaft of the machine is the lowest of the six shown. It drives by means of spur gearing roller number three, and through it the other rollers of the mill. No two rollers working together revolve at the same speed, and hence one rubs over the other, and they thoroughly grind the material between them. In the common three-roller mills it is necessary to pass the material to be ground through the mill twice, but in this machine one passage is sufficient, so that both time and floor space are saved, as the machine, it is claimed, does the work of two ordinary mills. Another noteworthy feature of this mill is that on No. 2 roller is a

lateral motion giving a sidewise movement of ¾ inch. This is also applied to No. 4 roller, and gives the same movement. Each roller can be separately and easily adjusted by means of adjusting screws. The fifth roller is the delivery roller. The weight of No. 2 roller is carried by a strong spring fixed between the bearings of rollers Nos. 2 and 3, so that by the movement of the adjusting screw, the No. 2 roller can be brought down upon No. 3 with the required pressure.

The principle of mounting the rollers of most machines, is that the centre roll shall revolve in fixed bearings, and the two outer ones shall revolve in bearings made to slide backward and forward in grooves in the framework. There is no means of adjusting the rollers in order to keep them in perfect parallel plane, or to compensate for the wear of the brasses. The consequence is, that immediately the bearings begin to wear, the rolls are not then in parallel plane with each other, and the longer they work the worse they get; until they only grind a small distance in the centre of the roll, causing the machine not only to perform imperfect work, but the rolls to wear hollow in the centre.

Hind and Lund, Limited, of the Atlas Works, Preston, Lancashire, claim that in their machine (Fig. 45) these defects are entirely obviated. The centre roll is mounted in a similar manner to other machines, but the two outer rolls are hung upon excentric studs at each side. Should the journals wear at all unevenly, this is at once detached, and by a single turn of the excentric stud at either one side or the other as the case may be, the rolls are kept always in perfect parallel plane.

This machine is fitted with relieving apparatus for throwing the two outer rolls apart whilst working, in case of accident, or for cleaning purposes. Thus the machine may be run for an indefinite period without the granite touching, hence no wear can take place; while the rollers may be instantly put back to their working distances, just exactly as they were before the rolls were thrown apart.

As will be readily understood, this is a very valuable improvement, as the machine can be put in and out of actual grinding work as often as may be desired, without once altering the pressure upon the springs or the grinding distances.

The bearings are all self-lubricating, and the most delicate colours or white lead can be ground without fear of being deteriorated. The machine too is almost noiseless. Many of them can be seen at work, and giving great satisfaction.

Brinjes and Goodwin’s machine is shown in Figs. 46, 47, and 48. The oil and pigments, having been measured or weighed, are placed in the trough _h_. This is provided with

stirrers, similar to those in a pug-mill, which are driven by means of the pulley _l_, _m_ being a loose pulley; by shifting the strap on to this, the machine can be stopped at once. When the oil has been thoroughly incorporated with the pigment, the mixture is allowed to run through the spout _g_ on the roller _a_. Working against _a_ is a second roller _b_, and this in its turn bears upon a third roller _c_. In order to prevent the grooving of the faces of the rollers, which always takes place when they revolve in the same plane, there is an arrangement by which a slight lateral motion is communicated to _b_, in addition to the rotary motion. A pin fixed upon the rigid bracket _k_ works in the grooved cam _i_, which is keyed on the shaft of the roller _b_. The grinding power of the machine is considerably increased by this modification. The rollers are worked from the pulley _d_; the loose pulley _e_ receives the strap when a pause in the working of the machine becomes necessary. The details of the construction of the grinding machine are given in Fig. 48. The rollers _a b c_ are constructed of granite or porcelain; for fine grinding, the latter substance is preferable. They are adjusted by means of the screws _g h_. These are furnished with spiral springs, so that should a nail or other hard substance get between the rollers, these can rise in their bearings, letting the nail fall down at the back. The “doctor” or scraper _f_ removes the paint from the surface of the roller _c_; _a b_ are also provided with smaller scrapers, which remove any paint that may cake upon their surfaces. Where extreme fineness is requisite, the paint is again passed through the machine, and this operation is sometimes repeated several times.

In working these or any other form of grinding rollers, great care must be taken to clean them thoroughly immediately after use. If the paint be allowed to dry upon the surface of the rollers it is difficult of removal, and interferes with the perfect action of the machine. Should the working parts become clogged with solidified oil, a strong solution of caustic soda or potash will remove it. By means of the same solutions, porcelain rollers may be kept quite white, even if used for mixing coloured paints. Although the colour of most pigments is improved by grinding them finely in oil, yet there are some which suffer in intensity where their size of grain is reduced. Chrome red, for instance, owes its deep colour to the crystals of which it is composed, and when these are reduced to extremely fine fragments, the colour is considerably modified.

PACKING.--When paint is not intended for immediate use, it is packed in metallic kegs. The construction of these, as made by B. Noakes & Co., is shown in Fig. 49. For exportation to hot climates, the rim of the lid is sometimes soldered down, a practice which effectually prevents access of atmospheric oxygen. White-lead paint is frequently packed in wooden kegs; these prevent the discoloration sometimes caused by the metal of iron kegs. When paint is mixed ready for use, it will, if exposed to the air, become covered with a skin, which soon attains sufficient thickness to exclude the atmospheric oxygen, and prevent any further solidification of the oil. The paint may be still better protected by pouring water over it, or it may be placed in air-tight cans. If it has been allowed to stand for some time, it must be well stirred before using, as the pigments have a tendency not only to separate from the oil, but also to settle down according to their specific gravity.