Do you know exactly how to choose an injection molding machine?

Time:2019-12-18 09:55:08 / Popularity: / Source:

How to choose an injection molding machine?
Procurement project of injection molding machine is not a small investment project; it is wasteful to buy a large injection molding machine, also it is too small to be used; therefore, how to choose an injection molding machine that meets needs of its own products becomes content of concern for each buyer. Gud Mould integrated multi-party data, edited a relatively simple and practical purchase considerations, hoping to give customers of injection molding factory a little good advice and help!
how to choose an injection molding machine 

First, according to specifications of injection molding machine

1. Calculate injection volume that injection molding machine should have based on weight of products made by injection moulding.

1) When plastic moulding articles is made of polystyrene (PS), injection molding machine should have a shot size of Wps:
Wps=(product weight + total gate system)÷(0.75~0.9)
That is Wps=(1.3~1.1)*(product weight + total weight of gate system)
2) If product is other plastic (named X plastic), according to above method, first calculate theoretical injection volume of this plastic as Wx:
Wx=(1.3~1.1)*(product weight + total weight of gate system)
However, it is not possible to simply use Wx to determine injection volume of injection molding machine. It must be changed to Wps value. Conversion formula is:
p - specific gravity of plastic
3) Another simple method to determine whether weight of shot is satisfied as follows:
W: Actual products made by injection moulding * Large weight (including weight of gate)
Wmax: mechanical screw * large PS shot weight
P: proportion of raw materials
As long as weight of product is less than calculated W, it is feasible. Taking HMD128M6-B screw forming PP material as an example, PS theory* shot weight is 239g, ie Wmax=239.
PP material density is 0.9, that is P = 0.9.
That is, as long as weight of PP product is less than 161g, 128M6B screw can meet requirements.

2. Calculate clamping force P according to vertical projection area of products made by injection moulding in template (head plate or seesaw)

Clamping force = clamping force constant * product projected area
Namely: P = Kp × s
P-clamping force (t)
S-Vertical projection area of product in template (cm2)
Kp-clamping force constant (t/cm2), Kp values are listed in the table below (Table 1)
Table 1: Clamping force constant Kp (for injection molding precision products)

3. Determine inner spacing of injection rod (guide post) from outer contour of mold; the latter is larger than the former.

4. Height of product determines mold opening stroke of injection molding machine; the latter should be 2 times larger than the former.

5. Other secondary factors

1) Modulus of injection molding machine should be compatible with height of your mold;
2) Thimble stroke, ejection force;
3) Process factors.

Second, purchase according to injection screw

how to choose an injection molding machine 

1. Standard screw selection

General injection molding machine has A.B.C three-speed screw, and some have four gears. Same type of machine A screw injection glue pressure is large, generally can reach about 190 ~ 210MPA, gram weight is small. C screw injection pressure is small, generally around 120 ~ 130MPA, gram weight is large. Generally choose type B or type C. Only when raw materials produced are thicker PE, PP or ABS products, C screw can be considered.
Following products must be selected with A screw:
Wall thickness is less than 1 mm thin wall. PC, ABS, nylon, steel and other engineering plastics, complex products, high precision. Due to design relationship, some products require side of product to be glued, and product flow length ratio exceeds 80 (ratio of distance from glue point to the end of product and thickness of product).

2. Special screw selection

1) PC-specific stainless steel or electroplated screw, some models can choose standard A screw plating.
PC special screw, small thread gradient, large injection pressure
2) SPVC, UPVC pellets
SPVC headless electroplating special screw and UPVC headless electroplating special screw are selected. In addition, high requirements are required to install a strong air cooling device on cylinder.
3) PA6, PA66 without glass fiber
Nylon special screw, part of nylon material can use a standard screw, but cutting speed is not as fast as special screw.
4) PA6, PA66 plus glass fiber
15% or less can consider ordinary double alloy screw with ordinary barrel, 15%-30% special double alloy screw with double alloy barrel, 30%-50% special full hard double alloy screw with full hard double alloy barrel.
Double alloy screw
5) PC color mixing and partial thin wall PP color mixing
Special color mixing screw, 268 or more models equipped with mixed color mixing head
6) Small weight transparent PC products
Small gram weight transparent PC product means that gram weight is less than 20% of weight of standard A screw. It is recommended to use a special small screw to shorten screw length to diameter ratio between 20-22:1. Prevent PC material from yellowing, darkening, and insufficient whiteness.

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