Distortion of sanitary wares after firing is one of the most frustrating issues faced by manufacturers . Often the reason is elusive and becomes an accepted part of the process.
This article will deal with one. Distortion after firing due to what is commonly termed the “slip meet”. It can be observed anywhere on the finished article where during the casting process the affected area was the highest point at which the mould became full of slip. In severe cases it can occur at the first meet of slip and carry on through the piece. A pedestal is a good example whereby a line can be observed at the face giving the impression of being produced from a cracked mould. Slip meets can also occur where hollow and solid cast areas of the item converge. The following solution should alleviate or at least minimise problems associated with these areas. WC can be effected at the front of the rim sometimes continuing back through the seat bolt holes and water inlet.
Wash basins can be distorted on the front bow as depicted in the sketch. Perhaps the most affected are solid cast or thin rimmed vanity basins especially where final installation is to a cabinet or worktop. Vanity basins are often sent for further process such as grinding, the piece maybe ground flush to fit the worktop however a visible hump is still left on the face of the fired item. A crack can occur at any of these points during fettling and sponging (clay finishing) and most manufactures leave untouched these areas until the piece is fully dried. Certainly this procedure is not followed 100% and intermittent clay cracking is the result.
As mentioned earlier in articles the method of Battery casting items has been a major leap forward in producing sanitary ware. Unfortunately the formation of the slip meet has become an intermittent problem that depends on many criteria.
The only permanent solution is to dissipate or remove the slip meet during the casting process. Some success has been achieved by adding another slip feed to the item, the downside being more tubing and valves for the operative to clean and maintain. It is difficult and problematic to add another slip feed to solid cast items as in Vanity basins and manufacturers yield and quality consistency varies according to the severity of the distortion created.
A permanent solution is to disperse or remove the ”slip meet ” this is achieved by changing the mould angle at least once immediately after the machine has been cast. For a stubborn or heavy slip meet the machine bench can be adjusted during the casting cycle as well. This will require a modification to the casting bench and its perhaps worthwhile to consider installing a Cell casting system as this procedure is carried out automatically during the production process.
Using offset cam bearings to adjust the machine angle from horizontal to the preferred angle offers the most precise lift. Air bag, air rams and hydraulic rams may not lift consistently especially if moulds of a different size are produced on the line. An additional advantage with the machine achieving a horizontal position is automated clay ware removal can be adopted.
We have discussed the reasons and Solution for the Distortion in the sanitaryware manufacturing process. If you find this article interesting and informative follow our Next article – solution to logo blur or break up for on-glaze transfer. Don’t forget to leave a comment below.