Ramming
The process of ramming moulds is by no means a simple operation. Inelegant and laborious as it may seem, it is at the ramming stage of the moulder's art that the foundation is laid for the successful achievement of task he undertakes; and nothing but sound judgment based upon intelligent practice is able to qualify the moulder in this particular department of his trade. See BUTT-RAMMER; PEEN-RAMMER.
Much subsequent repairing and finishing of the mould may be avoided when strict attention is paid to the necessity of ramming each portion of the mould in exact accordance with absolute requirements. For light castings of a duplicate character it is essential that the ramming be systematized in order that each casting shall be a true copy of its fellow in all respects, but particularly so in reference to weight, where due regard must be had to their being as light as possible. This of course can only be accomplished by discovering the point where the hardness of the mould surface interferes with an uninterrupted flow of the molten metal over it. Nearly all classes of light work may be successfully moulded without subsequent venting if due attention be given to the grading and tempering of the sand used, and ramming no harder than is absolutely necessary; careful tramping with the feet being all that is requisite in countless instances. The ignorant moulder pounds away, regardless of the differences consequent on whatever changes may be made in the material he works with. Not so the intelligent one: he is closely observant of all these things, and regulates his ramming accordingly. The admirable precision and duplication of similar castings produced on the moulding-machines furnish ample evidence of the truth of the aforesaid, as the whole process of moulding by this method consists in placing a measured quantity of sand in the flask every time to be operated upon by the rammer, which with mechanical precision presses it down into the flask and around the pattern with an exactness impossible of attainment by hand-ramming. It is very evident that whatever superiority machine-made castings possess over those made by hand-ramming, it must all inevitably result from the more efficient and exact ramming performed by the machine, as the entire operation consists of introducing an exact quantity of sand into the flask, bringing on the pressure, and withdrawing the pattern,--all of which operations are, in the majority of cases, performed automatically. Subsequent treatment of these moulds is limited to the placing of cores and closing the parts for casting, no hand-finishing whatever being required. See MOULDING-MACHINES. The ramming of heavy green-sand work undoubtedly calls for very superior ability, as not only must the mould face be made of the proper nature and density to resist the intense heat of the metal, but every suitable means must be employed to resist the constant pressure exerted whilst it remains in a fluid state. How to meet all these conditions and maintain a mould surface that shall be free from errors likely to produce faults in the resultant casting taxes the moulder severely when the material is not in all respects what it should be, and many are the contrivances invented to counteract or neutralize evils that are known to exist, as well as to provide against possible contingencies.
The nature and quality of sands changing with each locality renders it almost impossible to formulate absolute rules for ramming which shall be equally applicable at all places; it remains, therefore, with the intelligent moulder to observe well the kinds of sand he must work with, and regulate his ramming accordingly, remembering that with the finer grades there is always a possibility of ramming the mass to a consistency that will effectually prevent the escape of gases which form throughout the mould's surface when the metal enters therein; especially is this to be observed when the sand is of a clayey nature. See GREENSAND MOULDING; FACING-SAND; etc.
Ramming dry-sand moulds is not by any means as important as green sand, it only being required in this case to pack the sand firmly and evenly to the mould face, and of sufficient density elsewhere to permit of free handling and resist pressure from within. If the facing-sand be comparatively free from gas-producing substances, and the moulds are thoroughly dried, there is no necessity whatever for venting ordinary dry-sand moulds, there being no steam to lead away, as in the case of green-sand moulds. For this reason unskilled labor may, with some direction, be employed for ramming very many of the moulds made in dry-sand. See DRY-SAND MOULDING; DRY-SAND FACING; etc. Pit ramming is simply the process of packing the space between the mould and the pit wall with sand to prevent the pressure exerted within the mould from forcing out the walls; in other words, the pit is made to answer the purpose of confining the whole mould, just as flask does. A knowledge of the laws of pressure in moulds is very helpful to the moulder in this instance, because, knowing that pressure is greatest at the bottom it is at that point where the hardest ramming must occur, and every course of ramming may be made proportionately less dense as the top is reached, and consequently much valuable time saved in the operation. See TRAMPING; PIT; VENTING; BUTT-RAMMER; PEGGING-RAMMER.