The double-lock machine overcomes this difficulty by taking both yarn carriers across, one following the other, each on a pair of locks, each time the carriage moves across the machine. It is evident from this that every time the carriage is moved across the machine there are two courses put on the fabric, instead of one as with the single-lock machine.
Speed and Production
This point leads up to another advantage of the double-lock machine, that is, increased production on account of putting on two courses with each movement of the carriage across, as against one course with the single-lock machine. The production would not be twice as much, as might be supposed at first thought, for comparing two machines of the same size, the single lock could be operated at a greater speed than the double lock, but not approaching twice the speed. The reason for this is that the locks of the double-lock machine must, of course, be practically twice the length of the locks of the single-lock machine, and inasmuch as the locks must move far enough at each end to be clear of or past the needles, it is quite obvious that the double-lock carriage must have a longer travel. Therefore, it takes longer to complete one round of the carriage than the single-lock machine, to maintain the same needle speed.
This brings us to another point that may as well be disposed of here, and that is the speed of latch needle machines. Generally speaking, the maximum speed of a latch needle machine, either flat or circular, is governed by the needle speed; that is, the speed at which the cams raise and lower the needles, and the thread velocity, which is of course dependent on the needle speed.
Speed of Flat Machines
As a general rule, where the machine is in good condition and the yarn of fairly good quality, a flat machine with a crank drive should be operated at from 100 to 125 lineal feet per minute, and a chain drive may be operated at from 125 to 150 lineal feet per minute. The reason for this difference between the chain drive and the crank drive is that with the crank drive the movement of the carriage across the machine is not uniform throughout, its movement being faster in the center than at either end, therefore we must regulate our speed so it will not be too high at this point. On the other hand, the chain drive carries uniformly throughout the movement of the carriage except for two or three inches at the ends.
To explain what is meant by lineal feet per minute, let us assume that we have a 20-inch machine, that is, there are 20 inches of needles. In this case the carriage would have to travel about 30 inches on account of the locks having to clear the needles at both ends, therefore a movement of the carriage across and back, or one complete round, would cover twice 30 inches or 60 inches, or 5 feet. Now if we intend to run this machine at a speed of 120 lineal feet per minute, we would divide 120 feet by 5 feet, which would give us 24 rounds per minute, the speed the machine should run.
I do not wish to be understood as giving this as a hard and fast rule for the speed of machines, for there are many factors which enter into the operation of knitting machinery which might make it desirable to vary this speed. Some of these factors are the condition of the machine, the experience of the operator, the character of the yarn, the class of fabric, and sometimes the skill of the mechanic in charge of the machines.
Going back to the two-faced fabric, this must be made on one of the two cardigans. The “cotton backs” are usually made on the half cardigan, while the fabrics with two different colored faces are made on the full cardigan as a rule.
