Process and furnace for heat application

DETAILED DESCRIPTION There are several modes of carrying out the process of the present invention in which some of the details depend upon the product being made and the raw materials being worked.
The following is a detailed description of successful applications, including the best mode contemplated at present.
A detailed description of an apparatus specifically designed for carrying out the process is also laid out here.
The process diagram shown in FIG.
1 outlines the basic steps in the general process.
Since the process allows very close control of the preform heating, based on calculated and experiential air temperature and flow-rate data, optimal use of the process first requires a certain degree of pre-entry temperature control of the preform.
This pre-entry temperature conventionally depends not only on ambient temperature (control of which is inefficient) but also on the conduction rate from prior furnaces through the preform and its feeding mechanisms.
The effect of these factors is reduced in the process of the present invention by the step of bringing the temperature of the preform close to a "normalized" temperature just before it enters the furnace.
This will most often be a cooling step, although at some stages in the process and for some ambient conditions there may be mild warming.
The simplest embodiment of this temperature normalizing step 10 involves bringing more or less constant temperature air from a source and blowing it onto the periphery of the preform at the entry point to the furnace.
At the same time, the preform is fed into the furnace drawing chamber in a feeding step 11 using available feeding mechanisms.
These include motor driven drive screws.
The mechanism may include several of these drive screws if the core and a cladding or a plurality of claddings must be driven at different rates.
It is not necessary for these mechanisms to include rotating means.
Such means were a complicating expedient to achieve furnace uniformity as mentioned above and have had only qualified success