The common specifications of the screw are as follows:
1. The external diameter of the metric thread is in millimeters, such as 6,8,10,12,18,20 mm, etc., and the pitch is also in millimeters, such as 0.5,0.75,1,1.5,2,3, etc.
2. The outer diameter of the English thread is in inches, (= 25.4 mm per inch), such as 3/16,5/8,1/4,1/2, etc., etc., and so on.
The English pitch is represented by the number of teeth per inch.Set the caliper at 25.4 mm, align the tip of a ruler with the tip of the thread, and the other tip, such as aligning the tip of the thread, is the British thread. If the tip of the thread is not, it should be metric thread.
When measuring the pitch, it is best to put the tip of the thread on the white chalk. The marks on the chalk are clear and easy to measure.The metric pitch should measure a length, such as 10,15,20, millimeter, etc., count how many teeth are contained and calculate the pitch.
Thread specification is specified in inches for English thread, such as: G1."。Metric thread specification for metric thread, for example: M30.
The English system is an inch (2.54 cm) with how many teeth are fixed, usually 55 degrees.The metric system is the distance between the two teeth tips, which is the pitch of the MM, generally 60 degrees.
The general screw is divided into three parts, namely the feeding section, compression section and homogenized section.
Feeding area -- the base is small, and the main function is to transfer the raw material to the back segment, so it is mainly the problem of transmission capacity, parameters (L1, h1), and h1= (0.12-0.14) D.
Compression zone -- the bottom is changed, the main function is compaction, melt material, establishment pressure.The compression ratio of the parameters is equal to h1 / h3 and L2.Accuracy should be graded A= (h1-h3)/L2.
Measurement area -- the material of the compressed segment has been extruded to the front end of the screw, parameters (L3, h3) and h3= (0.05-0.07) D.
For the whole screw, the parameter L/D- length-diameter ratio.
Pros: L/D L/D and rotational speed n, is the screw plasticizing capacity and effect of the important factors of the L/D is material stay in the barrel for a long time, is advantageous to the plasticizing, flow pressure, leakage flow decrease at the same time, improve the ability of plasticizing, at the same time, higher requirements on the temperature distribution of material benefit, but the big, to use and have a negative impact on manufacturing and assembly, general L/D for the (18 ~ 20), but it has a tendency to increase.
Other pitch S, helix Angle phi PI Dtg phi, D = S commonly, the phi = 17 ° 40 '.
It has an effect on plasticizing ability. Generally speaking, it is faster to transport the larger one, so the shape of the material is different.Powder desirable phi about 25 °, cylindrical material about 17 ° phi, square phi = 15 °, but the different phi, for processing, is also more difficult, so the general phi take 17 ° 40 '.
E, for the material with small viscosity, e is as large as possible, too small and easy to leak, but too general assembly increases the power consumption, easy to overheat, e= (0.08 ~ 0.12) D.
All in all, in the present situation, there is no complete design method for the screw design due to the lack of necessary test methods.Most of them should be based on the properties of different materials, and the parameters should be set according to the experience to meet different needs.