Publication: Transactions of the American Ceramic Society
Columbus, OH, United States
DATA ON PLASTER MOULDS
GEORGE SIMCOE, Victor, N. Y.
In going over the subjects covered by papers in the transactions of the American Ceramic Society, nothing on the subject of Moulds can be found.
As this branch of the subject of pottery costs is a very important one, and one on which experience is general, it would seem that the subject should be started, and kept up till our records contain full data from every branch of the clay industry. The following little note is intended merely as a beginning, in the hope that it may bring in more valuable data from others.
The data here given is taken from the Locke Insulator Works, at Victor, N. Y.:
We have one mould maker, who turns out on an average of 80 to 100 dies per day. His wages are $2.40, and he uses from two to three barrels of plaster per day. The average consumption of plaster is about 700 barrels per year, which at $2.00 per barrel would amount to $1,400.00 for the plaster alone.
Our moulds vary in size from l"x3" to 30"x40", and in weight from 1 to 59 pounds. The wear and tear on them is very severe, because our ware must be even more solid than ordinary pottery, for cracks, however small, inside the ware, and not apparent on the outside, make splendid short-cuts for the electric current to break through. Our mould loss is increased very appreciably by "batting" clay into the moulds, and also the plunger process of forcing the clay into the mould causes much loss, due to rapid handling and great pressure. The following sketches show the cross section of one of the dies or moulds for making insulators:
The difference in ratio of breakage of moulds in the plunger and jiggering process is well shown in the following table, No. 1:
From this table, we see a wide variation in loss which may be accounted for, first, by the size, i. e., large moulds naturally break oftener than small ones, and second, by the process of filling, whether by jigger or by plunger machine. In order to economize on the cup, it is often found practical to increase or decrease the cross section of the mould, so that it will be interchangeable. However, this is not always a good policy, for the table shows that mould number 360-3s suffers a high percent, of loss, through the making of a large mould too thin.
The next table shows the number of moulds thrown out in the manufacture of a unit quantity of 1000 pieces of ware.
Table No. 2 as hardly comparable with Table No. 1, because the same number of moulds are not used at all times to produce 1000 pieces of ware. It has value, however, as it shows the location of leaks and their extent as represented by money, for from Table number 2, Table number 3 is deduced as follows:
To say what part of the cost of a piece of ware the mold represents is rather hard, but in the insulator business, I should say, from some careful calculation and estimation, that the moulds represent 1 percent, of the direct charge against the insulator. By direct charge, the actual cost, without any over-head proration such as salaries, office expense, advertising, insurance, etc., is meant.
In conclusion, I should like to ask representatives of the different branches of the craft to state through the Transactions what portion of their direct ware-making charge they assign to moulds.
Professor Binns: Mr. Simcoe wrote me for information on this subject, but his questions only covered the matter of breakage in moulds, and in my experience I never found the matter of breakage of much importance. Moulds would wear out, the surface being destroyed, but it was very seldom that a mould broke. He has a different proposition, where they are used under pressure. I think the matter of the wearing of moulds is highly important, and we need more data in regard to the proportions of plaster, amount of water, etc. A mould-maker puts plaster into water until he thinks he has got enough, but so far as I know, we have no data whatever to tell us just what amount of plaster and water to use in order to get moulds of a certain density. In my judgment, we need information on that point more than we need data on the question of breakage.
Mr. Watts: I want to say in regard to wear of moulds, that we think that we have that matter pretty well in hand in our plants. We do not have serious difficulty in the wearing-out of moulds. We generally make about one hundred moulds for a ten-thousand order. We have a system whereby a man reports every night the number of moulds of each size that he loses during the day, and within the shortest possible time, those are replaced for him. We make up about ten percent, more moulds than we give to the jigger-man, and he gets a mould replaced for every one broken. I do not think that one hundred moulds for ten thousand pieces is at all a bad figure. Our loss is, more than anything else, in the number of moulds broken, which I think can be directly traced to the design or application of the mould. I have seen that in the whiteware and other lines of business, where I was satisfied if the shape of the mould had been corrected a little, the loss would have been very materially decreased. Moulds are often made which we think are thick enough to do the work, but after a few days' use, we find we have but a few left, and common sense teaches us that we must change the design in some way.
Mr. Gates: In making terra-cotta, the sharp particles of grog which must be used, cut down the life of a plaster mould very severely, and hammering the clay into the mold makes its life very short. Our great trouble has been in getting any kind of uniformity in our plaster; even when getting from the same factory, different grades of plaster are sent in every carload. We have to use those plasters which are cheapest for us, and of course are cut off from the use of some kinds; but even from the same factory the plaster varies widely in quality. Our moulds in the terracotta business are each made for one special job or order, and each is discarded when that one order is finished. Rarely do we find that we can use a mould on two different orders. Consequently the mould department is with us one of the heaviest expenses in getting out work.
Mr. Weelans: As to durability of moulds, it may be said that much is dependent upon how they are cared for. We find that the life of a mould differs widely with different operatives, hence it is difficult to determine just how long a particular mould of any kind may last.
The cost of moulds is an important factor in any business, and particularly in the sanitary line, and we have often endeavored to improve the lasting qualities of plaster by an admixture of other materials, but with no success. It is not the wearing out of the moulds, in the common acceptance of that term, however, but the breakage, that most concerns us. Our moulds are for the most part very heavy and difficult to handle, hence they receive more abuse than the smaller moulds used in manufacturing table ware. To determine the life of moulds is, therefore, a very indefinite proposition, and one