Buying an injection molding machine for plastic cutlery is not a small investment. It is wasteful to purchase a big injection molding machine while it is not suitable if the size of the machine is too small. Therefore, what each buyer most concerned is choosing a suitable injection molding machine. There are recommendations for buying machine.

There are several factors which we should take into consideration, including the specification, and types of Injection Screws.

The specification of injection molding machine for plastic cutlery

According to the weight of injection molding products, we can calculate the injection volume of injection molding machine.

When injection molded products are made of polystyrene (PS), the injection molding machine shall have an injection volume of Wps.

Wps = (product weight + gate system total) ÷ (0.75 ~ 0.9)

Wps = (1.3 ~ 1.1)× (product weight + total gate system weight)

If the product is other plastic (named X plastic), the theoretical injection volume of the plastic should be calculated as Wx according to the above method:

Injection volume Wx:

Wx = (1.3 ~ 1.1) × (weight of product + total weight of gate system)

However, the injection volume of injection molding machine cannot be determined simply by Wx. It must be changed into its own Wps value. The conversion formula is:

Wps＝Wx÷p

Where p is the specific gravity of the plastic

Another simple method is to determine whether the weight of injection glue meets the following requirements:

W＝0.75~0.8*Wmax*P 

W: The maximum weight of the product that can actually be formed (including the weight of the glue mouth)

Wmax: maximum PS injection weight of screw

P: Specific gravity of raw materials

As long as the product weight is less than the calculated W, it is feasible. Taking HMD128M6-B screw forming PP material as an example, the maximum weight of PS theory is 239g, that is, Wmax = 239.

PP material density is 0.9, that is, P = 0.9.

W = 0.75*239*0.9 = 161(g)

That is, as long as the product weight is less than 161g PP material products 128M6B screw can meet the requirements.

2. 
   According to the vertical projection area of the injection product on the template (head plate or two plate), calculate the clamping force P

Clamping force = clamping force constant x product projection area
P＝Kp×s 
P－Clamping force (t) 
S－Vertical projection area of product on template (cm2) 
Kp－Mode-locking force constants (t/cm2) and Kp values are listed in the following table (Table 1)

3. The internal spacing of the pull rod (guide column) of the injection molding machine is determined by the outer contour size of the mold; The latter is greater than the former.
   The mold opening stroke of the injection molding machine is determined by the height of the product; The latter should be twice as large as the former.

The types of injection screw

General injection molding machine has A.B.C three - speed screw, some have four - speed. The same type A screw injection pressure is the largest, generally can reach about 190~210MPA, the weight of the minimum. C screw injection pressure is the lowest, generally about 120~130MPA, the weight of the largest. B or C are generally chosen. Only in the production of raw materials are PE,PP,ABS products thick circumstances, can consider the use of C screw.

A screw must be selected for the following products:

The thickness of the wall is less than 1mm. PC,ABS, nylon, Steel and other engineering plastics, complex products, high precision. Some products due to the design of the product side into the glue, and the product flow length ratio of more than 80 (into the glue point to the end of the product distance and product thickness ratio).

2. Special screw selection

1) PC special stainless steel or electroplated screw, some models can choose standard A screw electroplating.

PC special screw, small thread gradient, large injection pressure.

2) SPVC, UPVC granular material

SPVC headless electroplating special screw and UPVC headless electroplating special screw are selected. In addition, high requirements of products need to install strong air cooling device on the barrel.

3)PA6,PA66 without glass fiber

Special nylon screw, part of the nylon material can be general standard screw, but the feeding speed is not as fast as special screw.

4) PA6, PA66 and glass fiber

Below 15% can be considered ordinary double alloy 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.

NINGBO LISONG INJECTION MOLDING TECHNOLOGY CO.,LTD is a professional supplier for injection molding machine for plastic cutlery and we are try our best to offer a much lower wholesale price for our customers. What's more, we are a leading injection molding machine for plastic cutlery exporter who can give the overseas customers cheaper price and higher quality the same as the domestic customers. More information, please feel free to contact us.