Production of Decorative and Ornamental Rubber Products

Abstract

Abstract It is proposed to deal with the production of rubber goods which can lay claim to being decorative and ornamental, not according to their classification in a sales catalog, but according to the machines which produce them. CALENDERING One of the difficulties in a works handling rubber qualities ranging from pure gum stocks to the more heavily compounded variety, such as flooring, is to obtain sheets of the same thickness across the width. The wider the sheet the more difficult this becomes. With perfectly cylindrical rolls, the pressure of the rubber bank at the nip will cause the roll to bend, so that a sheet of rubber coming from between such rolls will be thicker in the middle. This variation is overcome by making the rolls a little thicker in the middle by only a few thousandths. However, the amount of bending depends on the type of stock being calendered, so that one calender cannot produce sheet of even thickness from all types of mixings. The greater thickness of the rolls in the middle compared with the ends is referred to as the camber. When the machine is under load, the camber corrects the bending so that the effect is equivalent to using perfectly cylindrical rolls that do not bend. Unless a firm has more than one calender for different types of stock, there is always one class of mix which cannot be the correct thickness right across the sheet. For many classes of goods this variation is not important, but for sheets of rubber intended for flooring to be cut to tiles and pure gum sheet to be cut to thread, it is obvious how important the question of uniform thickness becomes. One cannot expect mechanical pressure during vulcanization to correct this fault or, if it does, other effects are spoilt. For example, the marble pattern on flooring may be spoilt by a sideways flow of rubber under a powerful press, especially where considerable variation was present in the thickness of the calendered sheet. A recent method of correcting camber is to swing the top bowl of, say, a three-bowl calender, so that the axis of one bowl is at an angle to the one immediately underneath. The rollers are, of course, perfectly cylindrical, and only have to be swung through a few degrees.